I'm usually fine with the ac. just every now an then all things align like the sun not coming out that day so it gets cooler than expected. that's when I wake up to... snap! snap! maybe once or twice every couple months. pretty loud and sounds like it should hurt but doesn't. just have to be more causious and I'm not taking take it too lightly. don't ever want to have shot knees even though one of the has some issues from a childhood accident. I just take care to not stress it more than I should. also been working right so far... knock on wood!