The same as
get your shit together. Basically means calm down,
don't panic, or focus. Usually said if you are normally good at something, but aren't able to do it well because your mind is preoccupied with something else, or you're
just tired.
Kevin: Get your head on straight
Amit, my
grandmother could have gotten that
rebound.
Amit: Sorry man, I'm still tired from that party last night.