I used to have fairly serious problems with my wrist when I first started cubing, and even went to a doctor once about it.
I think your wrist hurts because you cubed for 14 hours straight without breaks. But if it hurts often though, and this isn't the first time it's bugged you, then try some of these:
1) Don't cube for long stretches without taking breaks. I try to do no more than 3-4 averages in one sitting. If I plan to do more, I'll take a break for 30 minutes before doing more speedsolves. Blindfold solving is a perfect way to keep practicing something, but give your wrists a break. It's not as intensive as speedsolving, but still fun.
2) If you wrist does hurt, and the pain doesn't go away after an hour break or so, then take a 2-3 day rest from cubing. Ice your wrist if it is tight or sore throughout the day after practicing. If after 2-3 days your wrist still bugs you, stop for 2-3 more days until it feels better.
3) You must use a good cube. I used to have wrist troubles all the time, but I know now it was because I was using a really crappy, barely prepared cube. Your cube should be relatively loose, and it should be quite easy to turn any single layer using just your index finger. If your cube is somewhat loose where finger tricks work, but it is still kinda stiff then this is exactly what is causing your wrist troubles.
Don't ignore the problem either. I cubed one day for about 10-12 hours straight with only minimal breaks and I had my wrist get to the point where simply moving it at all sent shocks of pain through my arm. Don't cube for multiple hours on a bad cube, only on loose ones. Ask anyone who has done a 24 hour marathon where even just one of their cubes was a stiff or semi-stiff cube. They all say they will never use a stiff cube again, ever.
Chris