What could cause someone to have a sudden blackout in vision?
A great question from a Healthtap patient!
Main causes of sudden black out: dehydration/illness, blood pressure drop, blood sugar drop (pre-diabetes/diabetes), vasovagal reaction, blood flow issue in brain (from dehydration, sugar level change, tumor of some type, intracranial pressure increase), seizure, medications, anemia, transient ischemic attacks/stroke, pregnancy.
Below is an even more complete list of causes of sudden black outs or syncope/fainting.
Syncope is a temporary loss of consciousness (fainting) that happens when the brain does not get enough oxygen. It comes on suddenly, only lasts for a short time and you recover fully within a short time. It is often called a blackout, faint or collapse. It isn’t the same thing as a seizure which causes jerking. It is important to seek medical attention if you suffer from syncope, as it may be due to a serious underlying problem. The most common causes are mentioned below.
What is syncope?
Syncope is when you become unconscious for a few seconds. It is also called fainting or passing out. You may feel sick and sweaty first or pass out with no warning at all. When you pass out, you fall to the ground. It isn’t the same thing as a seizure which makes you jerk. Usually, you come round after a few seconds and feel back to normal. Some people feel very tired after they’ve come round. Usually, syncope happens for a reason like when you’re in pain or have been standing for a long time in a hot place. It is very unusual for it to be due to any serious problem. The reason for syncope is that the brain needs a constant supply of oxygen and if that falls below a certain level, we fall to the ground until the more oxygen-rich blood can get to the brain.
How common is syncope?
Syncope is common at all ages and affects up to 4 in 10 people at least once in their lives. Most people never get medical help. Most people (95%) have their first attack of syncope before they’re forty years old. If you get it for the first time after 40, it is more likely to be due to a serious underlying problem. The most common cause is a common faint, also called neurally mediated syncope (NMS). Common faints usually happen for the first time in teenage years and affect girls more than boys. In older people, syncope is more likely to be due to underlying heart problems, low blood pressure or as a side-effect of their medication.
What problems can cause syncope?
This list does not include all the possible causes of syncope but lists some of the more common causes including:
Common faint (NMS): this is also known as vasovagal syncope. It is the most common cause of syncope. NMS can occur in various situations. These include fear, severe pain or emotional distress, after extreme exercise, during vomiting or when wearing tight collars that constrict the neck. During attacks, you may look pale and feel sweaty. Your eyes will usually stay open.
Orthostatic hypotension: this is a fall in blood pressure on standing up which can cause syncope. It can be due to medication prescribed to lower blood pressure, after prolonged standing, especially in hot places (which is why soldiers on parade may faint), as a result of neurological diseases such as Parkinson’s disease or after a big meal.
Cardiac syncope: this occurs due to an underlying heart problem. There may be a family history of sudden death. The syncope may be preceded by chest pain or palpitations and may happen after exercise.
What investigations might be advised?
The doctor will want to know more about what you were doing when you blacked out. You will be asked whether you’ve recently started new medication. Try to remember whether you had any warning before you blacked out. Did anyone see you fall? How did you feel when you came round? These details will help the doctor to make a diagnosis. Your doctor will examine you. They will check your heart, including your blood pressure when sitting and standing and your pulse. You may be asked to have an electrocardiogram (ECG). You may have blood tests for anaemia and diabetes. Further tests of your heart and nervous system may be necessary.
What else could it be?
The most common cause of blacking out is syncope. Other causes include epileptic seizures, psychosomatic syncope due to anxiety (psychogenic pseudosyncope) and other rare causes.
Other losses of consciousness may be due to low blood sugar (hypoglycaemia), lack of oxygen from a variety of causes (hypoxia) and over-breathing (hyperventilation).
You may also lose consciousness after a fall or blow to the head or due to excess alcohol or other drugs.
Strokes and mini strokes (transient ischaemic attacks) can also result in a loss of consciousness.
Prolonged unconsciousness, confusion after the event, incomplete recovery and tongue biting all suggest that the cause is not a simple faint.
What treatments may be offered?
Treatment will depend on the likely cause of your blackout. You may be asked to keep a diary of the circumstances in which it happened. Most cases will be managed by your GP but you may be referred for further investigation and treatment at a hospital.
What you can do if you feel like you’re going to faint?
- Lie down flat with your legs up on a chair or against a wall or sit down with your head between your knees.
- Squatting down on your heels can be very effective and is less noticeable in public.
- When feeling better, get up carefully. If symptoms return, resume the position.
- Discuss stopping any medication that may be responsible, with your doctor.
- Avoid alcohol.
- Drink plenty of fluids.
- Raise the head of your bed.
- Wear support stockings.
- Do leg crossing and arm tensing exercises.
Driving and syncope
Driving is not a problem for a simple faint but greater restrictions apply if the situation is more complicated or if diagnosis is less clear.
If in doubt, contact the Driver and Vehicle Licensing Agency (DVLA).
The DVLA does not have to be informed of a simple faint but failure to notify other conditions can lead to a fine.
What should you do next?
You should call an ambulance if you suffer from a blackout while exercising or lying down, if you have a family history of sudden and unexplained deaths or if you suffer from chest pain or palpitations. If the attacks recur or you do not make a complete recovery, you should also seek urgent medical attention. If you have lots of attacks, or you hurt yourself because of the faints, your GP may want you to see a specialist. They may also want a specialist to advise if your faints are affecting your driving. In all other cases, you should see your GP.
How can I avoid blackouts?
You will need to find the underlying cause and try to address it if possible. Common faints are by far the most common cause. Many people who faint know when it tends to happen and how to avoid attacks.
What is the outlook (prognosis)?
This depends on the underlying cause but is generally very good. In young people when the blackouts are not associated with any underlying heart or nervous system problem, there is no increased risk. In older people, any increased risk is due to the underlying condition and the risk from falling.