Is it permissible to cheat on exams due to severe forgetfulness and mental distraction, despite knowing the detestability of cheating and striving diligently in studying?

Deception and cheating are forbidden in Islamic law. This includes cheating on exams. Therefore, it is not permissible for a student to cheat on an exam, neither for themselves nor for others, because the Prophet's (peace be upon him) disavowal of cheaters indicates that cheating is one of the major sins. Forgetfulness does not justify cheating.