What is a blackout?

A blackout occurs when you faint - a period of unconsciousness - or when you suffer memory loss where you can't remember what you have just been doing. The medical term for an episode of fainting or blacking out is 'syncope'. Blackouts are very common with one in three people experiencing one or more episodes during their lifetime. 

What causes blackouts?

Blackouts can be triggered by many things, including...

  • Standing up too quickly after lying down ('postural hypotension' )
  • Frightening or stressful situations ('vasovagal syncope')
  • Arrhythmia
  • Excess alcohol intake
  • Side effects of drugs
  • Anaemia
  • Dehydration
  • Heart attack
  • Seizures
  • Strokes
  • Severe injury
  • Heart muscle or heart valve problems
  • Brain damage or infection
  • Epilepsy

The first two of these are common and do not indicate any underlying condition. Standing up too quickly causes 'postural hypotension' where the body does not adjust bloodflow quickly enough and not enough blood gets to the brain. Frightening and stressful situations can cause fainting due to 'vasovagal syncope' which again is an interruption of blood flow to the braindue to hypotension, and these episodes are normally very brief.

When should I see a doctor?

Anybody who suffers a blackout or who faints should see a medical professional to investigate the cause and to rule out any serious underlying condition causing the episode. Your doctor will generally check your heart rate and blood pressure and listen to your heart. Further tests may be required if the doctor notices something unusual and he or she may recommend...

  • An electrocardiogram (ECG)
  • Echocardiography
  • A stress test
  • A Holter Monitor
  • A 'tilt table test' where you lie on a tile table and your heart and blood pressure are monitored as the table is tilted