To lose your nerve is to find your courage gone at the last moment. Lose your nerve at the top, do not lose your nerve.
The timing is what matters, since the nerve was there until the moment it was needed. It is used of decisions as much as of heights.
1phraselose your nerveTo find your courage gone at the last moment.
“Do not lose your nerve when you get to the top of the board.”
lose your nerve is a phrase.
Practised in Idioms