I agree. just stick on some good music thatll cheer u up. Dont spend too much time on work. During the past month, i have been doing revision sessions that last till 4.30am, this means that i was revising for about 14-16 hours a day straight for days on end. The only way to get out of it is to sleep for like a week after.
Its best to take regular breaks (although i refuse to myself!). Arrange set times when u work till and set days with some mates, where u can go out down the pub/cinema/club, whatever u fancy.
U are on to something though, people have mentioned about being stressed about things for no reason. Some theories are that they are phsychic etc... personally i just think that your not 'finalising' things. So maybe you begin a task, but dont finish it to th extent that it plays on your mind.
Kind of a less extremem version of closure.... if u know what i mean.
Hope ths helps buddy.