What causes a blackout without no alcohol or drugs?

A seizure could cause a blackout. Other causes are possible, too, like a leak in a blood vessel in your brain. It is important that you get checked right away to find out what is going on.

Several possibilities, such as epilepsy, fainting due to vasovagal reactions, cardiac arrhythmias, dehydration, low blood sugar, to name a few. Strongly urge full evaluation. If you are having repetitive blackouts, avoid driving, use of power equipment, activities at heights, taking bath or swimming alone.