I had tendinitus, which was a result of doing several things at once: demanding electric guitar excercises, classical guitar (which of course is murder on your picking hand), and lifting weights. The first thing the psysiotherapist said to me is, "Stop lifting weights". So I did. The tendinitus didn't last too long, maybe a week or so without playing, and a lot less for a week or two after that. Then it was back to normal and there were no lasting effects.
Carpal Tunnel Syndrome (Tendinitus's big brother) is something much more serious. I've heard of CTS sufferers who couldn't turn a door knob, let alone play a guitar. My friend's dad had it way back when because he's a plumber and is always using wrists. He had the surgery and he STILL can't play like he did. Probably never will.
The only advice I can really give you is just to be vigilant about your hands. Have a good warm up including stretches before you start playing really hard. Give at least fifteen minutes at the start of a session to the practice of chords and other light stuff before you try and burn, you need to gradually work into the tough stuff. And being vigilant means staying away from other trouble areas for the wrists, so no video games! And if an old lady asks you for help carrying groceries to her car, say "No sorry, I have to watch my wrists"... well too far maybe.
