One may be narcolepsy, those irresistible sleep attacks that can hit multiple times a day.

WSJ: Unraveling the Riddle of Too Much Sleep

Narcolepsy is a brain disorder characterised by sleep attacks and abnormal eye movement which affects up to one in a thousand people.

BBC: Pill to boost brain power

Dr Alistair Benbow, medical director of SmithKline Beecham, said that ropinirole was associated with sleepiness, but only in a tiny minority of patients, and that the company had never previously come across patients who experienced sudden sleep attacks.

BBC: Parkinson's patients face sleep danger