The others have hit on my suggestions...ADs, and exercise and eating right...and LnL points out sometimes this just happens!
I will ask this...it has seemed to me that oftentimes action knocks you out of a funk...are there some small things you could tackle that would give you a sense of fulfillment? Like making "that" phonecall (whatever it is) or setting up an appointment or whatever.
How about a brisk walk around the block and then tackling two items on the list?
Sage
Relax. Appreciate. Be calm. Laugh. Enjoy. Be secure. Be loving. Be loved. Don't personalize. Don't ASSume. Accept. Be grateful.