My computer's intermittently going completely unresponsive. Thoughts?

Hi,

I'm on a 2009 Macbook pro, with no exceptional features. I just downloaded the latest software updates yesterday - 11/24/2011 - and I'm running OS 10.7.2.

The computer's been a little slower ever since I installed Lion, but since those last software updates, it's been unpredictably freezing. Trackpad and keyboard elicit no response, iTunes stops playing music, I (apparently) lose my internet connection. After ten seconds or a minute or three minutes, it goes back to functioning normally. Then, suddenly, it's frozen again.

I have no idea what's going on and no idea how to begin addressing the problem. I'd be happy to provide any other information about software or hardware or whatever that might be relevant ig you've all got any ideas about what might be going on.

Thanks so much for your time, and, I suppose, happy belated Thanksgiving (if you happen to be American).