My brain can't not think. I am always thinking about everything and anything, and I thrive at work when I have multiple projects to put my teeth into (like, 3 or 4 in parallel).
At home, I just keep going and going. The only way for me to get relaxation is by "drowning" my brain in one task, such as watching a movie, play a game, household chores (doesn't really work well, unless it's building something), or participate in sports.
I went to a psychologist to treat my claustrophobia (it really sucks when you can't be in a closed metal tube filled with chairs and lots of other people when you have to travel large distances) and she tried two approaches. One approach failed completely: she tried to make me "not think". I have no idea how to do that. She was saying things like, "close your eyes, sit relaxed, concentrate on your hand, feel it getting heavier, etc." I decided this wouldn't work for me when I caught myself thinking: "my hand has a constant mass, and I am not moving it. Therefore, its weight is constant, so it can't get heavier. No wait, scratch that, maybe the temperature in the room has just risen, then I will probably send more blood to my extremities to cool my body down, and..... wait, that's not the intention of this exercise."
(The other approach consisted of a method regulating my thoughts; this helped tremendously and I am proud to say that I can now fly without going into blind panick. Still don't like it, and still tend to avoid cramped or crowded places, but it's progress... Who would have thought that not all psychologists are quacks?)
Thinking rules.