I can't remember who (someone here at 3FC), but someone much wiser than I am gave me some advice about this. She said that you need to treat exercising not as an option, but as something you just do. Make it something that you just don't think about, you just do it... kind of like brushing your teeth. It would be like saying I don't feel like driving today, but I have to get to work, so I have to drive. You don't give yourself that option of not driving.
GO TO THE GYM!!! Otherwise, you might feel guilty later on tonight!
This time, I'm going to be stronger, I'm not giving in. - Rudimental