Epilepsy is periodic overactivity in the brain, and is known to give rise to cognitive impairment. In a recent study, we examined data from 42,000 people, examining the risk of dementia (Tai et al. Neurology 2026). Although epilepsy was a risk factor for dementia, poor sleep multiplied this risk considerably — i.e. much more than the additive effects of sleep and epilepsy. This was true both if you slept too much, or too little.