be out of (one's) head

1. slang To be crazy. He's out of his head if he thinks this plan is going to work! After yet another sleepless night, I'm starting to feel like I'm out of my head.

2. slang To be very intoxicated from drugs or alcohol. You were really out of your head last night! How do you feel this morning? A: "Do you remember anything you said to me at the party?" "B: "Not at all—I was out of my head last night."