My mother is forgetting a lot lately , she lost some of her skills.(she has some not strong epilepsy, she is under meds) what could that be sign of?

Immediately: Usually memory problems associated with personality changes as well as loss of learned skills happen in dementia, however they do evolve slowly and over time. When these symptoms happen relatively fast and are associated with other major symptoms like epileptic seizures then they warrant immediate attention. You need to book your mom with her doctor as soon as possible. Needs full evaluation.