A blackout is the sudden loss or near loss of consciousness and may be accompanied by dizziness, vertigo, headache or (if due to a fit/convulsion) shaking of the limbs and incontinence.

Causes

The most common cause is a simple faint which is the body's protective mechanism to ensure a sufficient blood supply gets to the brain. However HIV may affect the nerves that control blood pressure and result in dizziness or near blackouts when standing or sitting up quickly (postural hypertension). Some people with HIV get damage to the adrenal glands, usually caused by CMV, which reduces the production of corticosteroid hormones. Lack of these hormones is another important cause of postural hypotension.

A potentially more serious cause is a fit or convulsion as this might indicate an acute problem in the brain such as an infection or abscess, possibly a result of toxoplasmosis.

What to do

If a blackout has occurred it is important to tell your doctor or if the cause is definitely a fit to get medical advice urgently. It is useful to talk to anyone who witnessed the blackout to find out exactly what happened as this may help to determine the cause.

If the blackout was due to postural hypotension then treatment and advice can be given to help cope with this. If the hypotension is caused by adrenal damage, the treatment consists of hydrocortisone and fludrocortisone, normally given continuously to replace what the body normally produces. Doses will need to be increased at times when you have active infections.

Other possible causes of blackouts such as toxoplasmosis require specific investigation and treatment.