Happens to me too. I wouldnt freak out or anything, its probably muscle fatigue. I go through periods of mainly playing lead and the dreaded "shredding" stuff.... and when I go back to more chord based jazz playing my hands cramp up much more, and not while I'm playing, just after I'm done.
I alleviated some of the pain by trying to keep better wrist posture while doing the chording, its helped a bit, but I still get the pain every now and then.
I alleviated some of the pain by trying to keep better wrist posture while doing the chording, its helped a bit, but I still get the pain every now and then.