I always make room in my calorie count for chocolate, even though I'm staying at 1400 per day. I find, though, that when I crave chocolate and want to overdo it, I'm low on magnesium. If I take my vitamins regularly, the cravings don't get bad.
Low potassium triggers munchies, too. Potassium is in just about everything, and the only way you can be low is to have a low calorie limit where you literally can't eat enough in a day to get enough potassium and still stay under your calorie allowance. Unless you ate bananas all day long....