I have had that feeling where my head feels out of proportion or, like you said, my brain is too big for my head. But for me, it comes with a feeling that I don't know if it's normal or what. I've had this randomly since I was a kid. My head would start "buzzing", almost like my brain was buzzing, then it felt like the world sped up. People were talking faster, moving faster, as was I. It's like someone hit the fast forward button. Then, after 10 minutes, give or take a few minutes, it would end. Weirdest thing for me anyway.