The most common and most likely answer to this crossword clue is the 7 letter word SWOONED
I've seen this crossword clue in The Daily Telegraph
S
W
O
O
N
E
D
Buddy explains!

The straight part
We know that "collapsed" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case collapsed = swooned.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does SWOONED mean?
SWOONED verb- To faint, to lose consciousness.
- (by extension) To be overwhelmed by emotion, especially infatuation.
- To make a moan, sigh, or some other sound expressing infatuation or affection.