Usage of getting into his head
The idiomatic expression “Get into someone's head (get into (one's) head)” is used with the following meanings:
To begin to understand how one thinks.
- You need to get into the criminal's way in order to find a way to stop him.
To intentionally disrupt or undermine one's focus, confidence, or performance.
- The opposing coach called a time out at the last second to try to get into the kicker's head.
You are probably looking for the idiom:
go to someone’s head
to confuse, excite, or intoxicate someone.
(Collins Dictionary)