1. to fall (over, down), to collapse, to take a fall, to topple
2. to be destroyed (in a collapse), to collapse, to cave in, to crumble, to give away
3. to be confined to bed (with an illness), to come down with, to break down (e.g. from overwork)
4....
1. illness (usu. excluding minor ailments, e.g. common cold), disease, sickness
2. bad habit, bad behaviour, weakness, failing
3. crazy, insane, disturbed, sick in the head