Sometimes we hit a slump, I'm currently stuck in the rhythm of the seasons - winter is for resting. Although I'm still going to the gym too, sometimes a small break from your training is a good thing. You don't need to feel guilty or force it, the desire will come back on its own. This past week I've been re - watching my DB DVDS and some other FMA instructionals giving me some food for thought and ideas for training/drills/stick work/etc. When I'm ready to start regular training again I'll be on GO.
Another consideration is to make your martial arts training a part of your daily routine. Until a few weeks ago, I would just play with the sticks for 20 min a day. It's kind of like my meditation. Sometimes it's serious, but mostly it's just playing around to relax. No need to be pumped up, just sort of chill. Even with the heavy bag, just turn some relaxing music on and play at different striking combinations. It'll help ease your return to more intensive training.