I don't know that there's a universal answer to this--you have to listen to your body. That said, exercising frequently (daily, or 5-6 days a week) is a very good thing. It's possible that your body was just holding onto water with the exercise last week, but it will get used to it. If you feel really exhausted you could skip 1 workout, but no more than that.
If you're feeling hungry, it might be necessary to re-evaluate your diet. (I've found that when I start exercising after an extended hiatus, I'm starving afterwards. But after a couple of weeks my body acclimatizes and the post-workout hunger becomes more moderate.)