Collapse, faint (4,4)
I believe the answer is:
keel over
This clue is a double definition.
'collapse' is the first definition.
(I've seen this before)
'faint' is the second definition.
(I've seen this in another clue)
(Other definitions for keel over that I've seen before include "Suddenly collapse" , "Capsize" , "Fall, as in a faint" , "Pass out" .)