Thumb lost all strength? What happened?

My girlfriend bought me a PlayStation 3 for my birthday (I know, pretty kickass girlfriend). Ever since, I've been almost addicted to it. Some days, while my girlfriend is at work, I'll be playing it 5 to 7 hours a day with frequent, but short breaks. Other days, I'm spending precious time with her, with an average max usage of 2 hours. Anyways, all those details are probably completely useless..sorry 'bout that. Anywho, yesterday night the lady was out with friends, so I was playing LittleBigPlanet. Eventually, I noticed that when I tried popping my index finger with my thumb, I couldn't do it. It was like my thumb had forgotten how to do it. I tried and tried and started freaking out. It was REALLY weird, and I proceeded to turn off the game for the night. An hour later, my thumb had lost 90% of it's mobility and strength. I could barely bend it let alone wiggle it. Thankfully, I woke up this morning to find that more than 70% of mobility/strength was back. Right now, it's almost completely back to normal. I'm really baffled because I've been playing FPS's on my home-built gaming computer for years. I apologize, I ramble quite a lot. If anyone is reading this, and either is a medical expert, or had this happen to them, and managed to read this without falling asleep on the keyboard. Can you please help me figure out what the hell happened? I'm completely clueless. Also, provide info on how I can avoid it.