Sounds like the blahs. I usally get them once I complete a project and need to start the new one, but just don't want to. Do something fun to take your mind off of everything for a little while. Read a magazine, pick up a good book, watch or go to a good movie. All of those things will help relax you and your mind too. It'll make you feel better and ready to tackle the world. Go out for ice cream! That's a good one for me especially if it is chocolate. There is nothing better to take your mind off of wat ails me than chocolate!
Let me know if any or all of this works! Hope you feel better soon!