Blackouts are periods of memory loss or unconsciousness. This condition is described as a lack of awareness or a period of unconsciousness when you are unable to recall what you did or what happened. Excessive alcohol consumption, drug side effects, brain damage or disorders which are affecting your brain function such as epilepsy can lead to blackouts. Syncope is also known as fainting which is a term that is used to refer to a blackout. 
There are many conditions which can cause syncope such as a condition which is known as postural hypotension (this is a condition in which a person faints after standing up quickly from a lying position and there is not sufficient blood flow to his brain at that point), abnormalities of the heart muscle or valves and cardiac arrhythmias (abnormal heart rhythm or rate). The vasovagal syncope is a generally harmless form of blackout. In this condition there is a disruption in the balance of the neurotransmitters which are regulating your heart rate and blood vessels which are causing a temporary decrease in the blood flow to your brain. This is a very common cause for fainting which even can occur as a reaction to frightening or stressful situations. It is typical to return the full consciousness promptly. Also there are some cases in which blackouts are happening due to traumatic event in which you may forget everything that happened right after the event (anterograde amnesia) or right before the event. Blackouts that appear due to trauma or injury or unexplained blackouts should be treated by a medical professional. 
Blackouts can happen as result of many other symptoms which depend on the underlying disorder or cause. There are some cases in which the memories from the blackouts can be recovered but also there are other cases in which they cannot be recovered. Also there are some cases in which blackouts can lead to problems forming new memories. If your blackouts cause you concern or they recur, then you should ask for medical help.
What other symptoms might occur with blackouts?
Blackouts may accompany other symptoms which are affecting your brain and nervous system such as
- Muscle twitching, spasms or seizures
- Memory loss
- Loss of vision or change in vision
- Head injury
- Dizziness or vertigo
- Difficulty speaking
- Changes in mood, personality or behavior
- Changes in hearing, taste or smell
Other symptoms that may occur along with blackouts: Blackouts may accompany symptoms which are related to other body systems such as
- Weight loss
- Nausea with or without vomiting
- Body aches
Serious symptoms that might indicate a life – threatening condition: Also there are some cases in which blackouts are a symptom of a life – threatening condition and in this case you need to seek medical help.
What causes blackouts?
- Traumatic causes of blackouts :
- Traumatic emotional event
- Phlebotomy (drawing a blood sample)
- Mild head injury
- Injections and inoculations
- Electroshock therapy
- Complications of brain surgery
- Substance – related causes of blackouts [3,4]:
- Recreational drug use
- Poisons such as cleaning chemicals or pesticides
- Medication side effects such as the side effects of cancer treatments or seizure medications, or argent used for anesthesia
- Alcohol intoxication
- Disease and disorder which can be causes for blackouts:
- Vasovagal syncope
- Postural hypotension
- Parkinson’s disease (brain disorder that impairs movement and coordination)
- Nutrient deficiency
- Infections of the brain
- Epilepsy (disorder characterized by recurrent seizures)
- Encephalitis (inflammation and swelling of the brain due to a viral infection or other cause)
- Dementia 
- Dehydration (loss of fluids and electrolytes which can be life – threatening when severe and untreated)
- Cardiac arrhythmia
- Brain or spinal cord injury or tumor
- Serious or life – threatening causes of blackouts:
- Traumatic injury
- Severe infection
- Myocardial infection (heart attack)
- Heart valve diseases and disorders
- Cardiomyopathy (weakened or abnormal heart muscle and function)
- Arrhythmias (irregular heartbeats)
 Fitzpatrick AP, Cooper P. Diagnosis and management of patients with blackouts. Heart. 2006;92(4):559–68.
 Iribarren J, Prolo P, Neagos N, Chiappelli F. Post-traumatic stress disorder: Evidence-based research for the third millennium. Evidence-Based Complementary and Alternative Medicine. 2005;2(4):503–12.
 White AM. What happened? Alcohol, memory blackouts, and the brain. Alcohol Research & Health. 2003;27(2):186-96.
 Fernandez AC, Gicquelais RE, Jannausch M, Bohnert ASB. The role of drugs in alcohol poisoning and blackout events: A latent class analysis of a residential treatment sample. Alcoholism. 2019;43(11):2431-7.
 Robitzski D. Research links blackout drinking to doubled dementia risk. Neoscope. 2020.