Once when I was about 10. My mum had an epileptic fit, but a) because I was young, and b) because she hadn't discussed the condition and I hadn't heard of it at that time, I was really scared it was something very serious, so I phoned 999 and asked for an ambulance.
She'd re-gained consciousness by the time the ambulance arrived, but was still in that confused state. Was a distressing situation all round.