I sometimes get so into drawing that I forget the time, yes - but luckily, my stomach is a little monster that will not be denied, and when I get to hungry, I simply lose the ability to draw. Thus, I eat regularly.
One thing I have consciously had to do, though, is to take regular breaks. Once every 20-30 minutes, get up and walk around, stretch out my shoulders and my wrists, etc. While I have never had any carpal tunnel syndrome-symptoms (due to the way I hold the pen, I assume; it's kind of odd and different from most people, and thus does not put the same kind of strain on my hands), I do have issues with muscle-cramps in my shoulders - and to keep those from bothering me, I have to get up and move around.
Speaking of carpal tunnel syndrome - this is a very serious issue, and EVERYONE who spends a lot of time drawing should pay attention to it. Stretching and relaxing your wrists is super-important. Getting CTS will not only ruin your ability to draw, it will seriously incapacitate you. I mean, you use your hands for a LOT of stuff!