Transient global amnesia is identified by its main symptom, which is the inability to form new memories and to recall the recent past. Once that symptom is confirmed, ruling out other possible causes of amnesia is important.

These signs and symptoms must be present to diagnose transient global amnesia:

• Sudden onset of memory loss, verified by a witness
• Retention of personal identity despite memory loss
• Normal cognition, such as the ability to recognize and name familiar objects and follow simple directions
• Absence of signs indicating damage to a particular area of the brain, such as limb paralysis, involuntary movement or impaired word recognition

Additional symptoms and history that may help diagnose transient global amnesia:

• Duration of no more than 24 hours and generally shorter
• Gradual return of memory
• No recent head injury
• No evidence of seizures during the period of amnesia
• No history of active epilepsy

The underlying cause of transient global amnesia is unknown. There appears to be a link between transient global amnesia and a history of migraines, though the underlying factors that contribute to both conditions aren't fully understood. Another possible cause is the overfilling of veins with blood due to some sort of blockage or other abnormality with the flow of blood (venous congestion).

While the likelihood of transient global amnesia after these events is very low, some commonly reported events that may trigger it include:

• Sudden immersion in cold or hot water
• Strenuous physical activity
• Sexual intercourse
• Medical procedures, such as angiography or endoscopy
• Mild head trauma
• Acute emotional distress, as might be provoked by bad news, conflict or overwork

Interestingly, high blood pressure and high cholesterol — which are closely linked to strokes —are not risk factors for transient global amnesia. This is probably because transient global amnesia doesn't represent blood vessel diseases of aging. Your sex doesn't seem to affect your risk, either.

The clearest risk factors are:

• Age. People age 50 and older have a higher risk of transient global amnesia than do younger people.
• History of migraines. If you have migraines, your risk of transient global amnesia is significantly higher than that of someone without migraines.

Transient global amnesia has no direct complications. It's not a risk factor for stroke or epilepsy. It's possible to have a second episode of transient global amnesia, but it's extremely rare to have more than two.