I recently heard a motivational speaker liken the 'racing mind' to the 'a drunken monkey that lives in my head'.

He described how the drunken monkey is constantly telling him he should be doing this or
he has forgotten this or what the hell are you going to do about that, even waking him up at all hours of the night with another message.

Gosh it made me laugh. A drunken monkey is such a good way of describing it.