Check out this very thought-provoking (assuming you can still form thoughts) article from Stephan Kesting of Grapple Arts:
Lest you think this is a perfect excuse not to come to Fight class, here’s a key point:
“For the recreational MMA practitioner the danger probably isn’t that great. You’re not getting hit as often or as hard as the professionals. But PLEASE remember that you DON’T need to be in an all-out slugfest every time you train. There are ways to develop all the technical skills using drills and controlled, light-contact sparring. And if you crave the feeling of complete exhaustion and having been put through the wringer I’d suggest that you do it with grappling rather than kickboxing.”
See also “How Hard Should You Go During Sparring?”