Hand cramp

I can't stop playing Skull Stax! It's just so soothing...click,click, click. I always play with the monster faces & the eyes follow your mouse. Genius. The only problem is that it doesn't get harder once you hit a certain point & therefore the last few times I've played I got to 100+ levels, 1 million + points and a hand cramp. I forced myself to read over lunch at work- luckily I'm at a really riveting part of the book (The Shadow Rising, Book 4 of Robert Jordan's Wheel of Time series which I've ready several times already - just keep getting hooked!) - because yesterday I just played Skull Stax the whole hour, got home & played all evening. Ack! Tonight will be different because I'm stopping for, well till at least tomorrow. Really!