'paroxysmal' originates from Medieval Latin and Greek, specifically from Greek 'paroxysmos' meaning 'a sharpening, excitation, or sudden attack'.

'paroxysmal' came into English via Late Latin/Medieval Latin 'paroxysmus' (from Greek 'paroxysmos'), and developed into the modern English adjective 'paroxysmal'.

Initially it referred to 'a sharpening or sudden excitation' (in physical or emotional sense); over time it came to mean specifically 'sudden attack or episode' as used in medical and general contexts.