I find that when I turn the lights out and try to sleep and can't, if I turn the lights on and try to read a book, I conk out. The WORST thing is TRYING to go to sleep. Do something you enjoy that is relaxing. The important thing is to enjoy your time off and don't WORRY!

Cat naps are beneficial. You have a war-time mentality. People in combat situations often can't sleep through the night and have to take cat naps. Eventually, the war will be over and you can get back to a normal sleep cycle, but until then, sleep when, and for however long you can, and don't think you HAVE to get a full 8.