You are probably havng Nausea because you are so tired, go to bed at a reasonable hour, dont eatnor drink a lot before bed. You say you think too much so you need to learn to switch off when you go to sleep, you can use visualisation for this, think of a really nice place you have been to ,or know, a garden /beach/ somewhere quiet and calming that you love to be, so picture that place ..your special place where you are happy.. you are walking there let your eyes dwell on it all, smell the ocean or the flowers...stay there...its pleasant. Do the same thing every night do not let your mind wander, if it does go back to your place., you will get into the habit and fall asleep..good luck