Symptoms of fainting from low blood pressure

As blood is pumped by the heart around the body, the pressure with which it pushes against the walls of blood vessels changes.

When the heart is squeezing blood into the arteries, the pressure is high. When the heart is relaxed, the pressure is lower.

Your blood pressure is a measurement taken of the highest reading and the lowest reading. It is given as 2 figures — highest over lowest. Blood pressure is measured in ‘mmHg’, which refers to millimetres of mercury.

What is low blood pressure?

Low blood pressure is also known as hypotension.

Most doctors would say that you have low blood pressure if it is below 90/60 mmHg. Your doctor will refer to this as ‘90 over 60’.

Is low blood pressure a problem?

For some people, low blood pressure is a sign of good health. These are generally people who are very fit and who have a slow pulse. For other people, low blood pressure is a problem.

Often, people with low blood pressure can be expected to lead longer lives.

However, people who experience continuing symptoms of low blood pressure should see a doctor. Sudden, severe low blood pressure (shock) can be associated with serious medical conditions.

What are the signs and symptoms of low blood pressure?

The symptoms of low blood pressure may include:

• light-headedness
• dizziness
• weakness
• blurry vision
• pale, clammy skin
• fatigue
• fainting

These symptoms can occur when doing nothing. They are more likely to occur when changing position, such as standing up or when straining on the toilet.

However, often there are no symptoms and low blood pressure is often only identified as a result of a routine medical examination or during the course of an investigation for some other condition or underling illness.

Low blood pressure may be more serious in elderly people who may have an underlying illness or who may be at risk of a fall.

Check your symptoms with healthdirect’s Symptom Checker to get advice on when to seek medical attention.

What causes low blood pressure?

Apart from being very fit, people can have low blood pressure if they:

• are overheated, either from the weather, from hot baths or showers, or from wearing too many clothes
• have too little blood circulating, either from donating blood, from bleeding heavily, or from being dehydrated
• are pregnant
• are taking one of many different types of medicines
• have a lot of drugs or alcohol in the system

People can also have low blood pressure due to medical conditions, such as if they:

• are having an allergic reaction
• are seriously ill with an infection
• have certain heart conditions
• have a disorder of the nervous system or glandular (endocrine) system
• are in severe pain
• have nutritional deficiencies

There is also a particular type of low blood pressure called ‘postural hypotension’ or ‘orthostatic hypotension’. In this condition, a person’s blood pressure is normal when they are sitting or lying down, but it drops suddenly when they stand, making them feel dizzy or lightheaded. This can also occur when standing too long without moving.

Postural hypotension is fairly common, particularly in older people. It can be caused by one of the situations or conditions listed above. If it happens often, or if it causes problems, you should see your doctor about it.

When should I see a doctor?

If you think you might have symptoms of low blood pressure listed above, it’s best to see your doctor.

How is low blood pressure treated?

If there is an underlying cause for your low blood pressure, and it is giving you problems, you may need treatment for that underlying cause. But if it isn’t causing you problems, treatment won’t be needed.

Your doctor may advise you to take precautions to prevent episodes of low blood pressure, such as avoiding dehydration, hot showers or standing up too quickly.

Low blood pressure, also known as hypotension, is when you have a blood pressure level that is below the normal range.

If your blood pressure is naturally low, this probably won’t cause you any problems and won’t need treating. In fact, the lower your blood pressure, the lower your risk of heart disease and stroke.

Low blood pressure can sometimes be caused by medications or can be a sign of another health problem. This can sometimes cause problems such as falls, fainting and feeling dizzy, so it might need looking into and treating. Speak to your doctor or nurse if you’re worried about low blood pressure.

Plus, take a look at the animation below on how to manage low blood pressure when you stand up.  

What are the symptoms of low blood pressure?

Low blood pressure often has no symptoms, but can sometimes mean that not enough blood is flowing to your brain or organs. This can cause symptoms such as:

• feeling dizzy, faint or light-headed
• feeling unsteady
• feeling sick (nausea)
• blurred vision
• a general feeling of weakness
• feeling confused
• suddenly noticing your heartbeat (palpitations)
• fainting

If you have these symptoms, stop what you’re doing and sit down or lie down in case you fall, and drink some water.

Speak to your doctor or nurse if you experience these symptoms. As well as being unpleasant, they could mean you’re at risk of having a fall. They could also be a sign of another health problem.

Low blood pressure when you stand up

Sometimes, changes in your posture can cause your blood pressure to drop, for example, going from sitting or lying down to standing up. You might feel the symptoms listed above when you stand up, such as feeling dizzy or faint. They will pass quickly as your body adjusts, but can put you at risk of falls.

This is called postural hypotension or orthostatic hypotension. It’s caused by changes to your arteries which happen as you get older and if you’re taking medications to lower your blood pressure. 

The animation below provides information on the causes, symptoms and potential interventions related to orthostatic hypotension.

This film was produced by Newcastle University for work completed by Dr James Frith, supported by the NIHR Newcastle Biomedical Research Centre. 

What causes low blood pressure?

Some people have a blood pressure level that is naturally low. That is, there is no specific cause or reason why. It can be the result of a healthy lifestyle and being fit and active, and your genes may play a role.

Your blood pressure varies throughout the day. It might drop when you’ve just eaten while your blood is carried to your gut, if you’ve been standing up for a long time, if you’re dehydrated, and if the temperature is warm.

There are a number of other possible causes of low blood pressure:

Medications
Low blood pressure, and low blood pressure when you stand up, can be caused by medications. These include medications to lower blood pressure, antidepressants and beta blockers, which are used to treat heart problems. 

Health problems
Low blood pressure can also be caused by an illness or health problem.

• Diabetes can affect the normal control of blood pressure because it can affect your hormones and the nerves leading to your blood vessels. If the nerves are affected your blood pressure might drop when you stand up because your blood vessels can’t adjust to the new position quickly enough.
• Neurological conditions (conditions which affect the nervous system).    For example, Parkinson’s disease. These can affect the autonomic nervous system which controls the things our body does without us thinking, including the widening and narrowing of the blood vessels. If your blood vessels are wider, your blood has more space to flow through so your blood pressure falls. The drugs that are prescribed to treat Parkinson’s can also cause low blood pressure, particularly postural hypotension.
• Problems with your adrenal glands. For example, Addison’s disease, an infection, or a tumour. The adrenal glands sit just above your kidneys and produce hormones which help to control your blood pressure. If they are damaged, this can cause a drop in these hormones and a drop in your blood pressure.
• Neurally-mediated hypotension.  This is when you have been standing up for a long time and your body sends signals to your brain telling it that your blood pressure is high, when in fact it’s too low. Your brain then signals to your heart to slow down, and your blood pressure falls lower.
• Heart problems.  Heart problems such as heart failure or hearts attack can lead to low blood pressure as the heart can’t pump blood around the body as well as it should.
• Anaemia. This is where your red blood cell count is lower than normal, or the amount of haemoglobin – the part of the blood that carries oxygen – is lower than normal.
• Serious injury and shock. Serious injury, burns, and going into shock can all cause your blood pressure to drop. For example, if you lose a lot of blood if you have an allergic reaction called anaphylactic shock, or if you have shock caused by a bacterial infection.

How is low blood pressure diagnosed?

Like high blood pressure, low blood pressure (hypotension) can be diagnosed easily with a blood pressure check.

If you feel dizzy or faint when you stand up, you might need to have your blood pressure measured when you’re lying down and again while you are standing up.

You might be offered a tilt table test. This is where you lie on a table that starts in a horizontal position, then slowly tilts so that you’re in an almost upright position – as if you were standing. You will have your blood pressure and pulse monitored, and any symptoms you feel will be recorded. You might also have a blood test to check the levels of certain hormones.

What is a low blood pressure reading?

A blood pressure reading below 90/60mmHg is considered low blood pressure. Only one of the numbers needs to be at this level or lower to count as low blood pressure. Read more about what the numbers mean.

How is low blood pressure treated?

If your blood pressure is naturally low and isn’t causing you any problems it probably won’t need any treatment. If you have symptoms and your doctor or nurse feels that you would benefit from treatment, they will try to find the cause of your low blood pressure so that they can find the best way to treat it. 

The treatments will vary depending on the cause.

• A change in medications. If your GP thinks that your blood pressure is caused by a medication you’re taking they might want to try an alternative medication or a different dose.
• Hormone replacement. If your low blood pressure is caused by a change in certain hormones, for example if your adrenal glands have been damaged, you may be referred to a specialist called an endocrinologist. They might prescribe hormone replacement medication.
• Medicines to stimulate your nerves. If you have a neurological condition, you may be given medicines to stimulate the nerves.
• Medicines for low blood pressure. These medicines narrow your blood vessels or expand the volume of your blood to raise your blood pressure. These are very rarely needed, as the treatments listed above and the changes you can make for yourself are usually enough.

What can I do for myself?

There are other things you can do for yourself to help with your symptoms.

• Wear supportive elastic stockings (compression stockings). They put extra pressure on your legs which helps to improve circulation and raise your blood pressure. For some people this can be enough, but speak to your GP first because they aren’t suitable for everyone.
• Stand up slowly from sitting or lying down. You can try other simple movements to get the blood flowing before you stand up, such as straightening and bending your legs.
• Avoid standing for long periods of time. 
• Drink enough water throughout the day, around 2 litres, so you don’t get dehydrated.
• Eat little and often throughout the day. This avoids low blood pressure after eating. 

Read more
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