off one’s head—(coll.) crazy or behaving as if mad (also: out of one’s head):
- He must be off his head to go jogging in this weather.
Note: The expression does not correlate in meaning with the phrase off the top of one’s head—(coll.) without proper consideration; in an impromptu manner:
- He was impetuous and inclined to think off the top of his head at times.
off one’s mind—
1. said of smth. no longer causing worry or anxiety:
- And he had felt so happy…. His confession to June was off his mind.
2. = off one’s head:
- Politics is dirty. If so, one must be off his mind to enter politics.