Penny is furious and more than a little freak out with Sheldon and Leonard when they sneak into her apartment overnigh, and cleaned it  when she is sleeping. This is the synopsis of episod 2 of season 1. It seems that Sheldon has some kind of obsessive-compulsive disorder. When he saw penny's room messy it even made him insomnia and can't fall into sleeping.It is so interesting.