NatalieJo,
I get that way too, often. It usually happens for me on Mondays and Tuesdays, and is (I have found) a result of eating (lots of) unhealthy food over the weekend. So maybe that's what's up with you, too?
If you don't feel like walking outside, maybe stay inside and at least pace the house during commercials or doing an exercise DVD or catching one of those exercise shows on TV (I don't know if you get those, I think I used to). The important thing is to keep moving some way. The longer you stay put the more down you might get.
I hope you climb out of the rut soon and get back to happy! I'm pulling for ya!!
amber
