Take a day off. If you try and practice when you're in a bad mood you'll only frustrate yourself more. Some people believe that if you practice when you're not in the right head-space you could actually make yourself a worse musician.
If you're having a rough day and you don't have to play, don't. Put the horn down and tomorrow's another day. Now, if you sound bad for longer than a day or two you might have more serious problems and you should spend some time with a pro.
...but I think you'll be okay tomorrow.
