The expression `getting out of your head` refers to not thinking, letting go of preconceived ideas (which your co-players obviously are painfully unaware of). Goes with the expression `being in your head`: not being `in` the scene, but thinking about what you should be doing/saying/playing.
Improv works best if you just let it happen and don`t think about it too much or too hard. It works best is you`re not in hour head.
If you`re gonna stink, stink out loud --- NN