Mid-2010 MBP keeps freezing, lags when restarted.

My 13 inch MBP has been messed up the past couple days. When using Safari, it will randomly freeze. Everything freezes. I can't even quit Safari to see if that's the problem. I have to do a hard reset with the power button, and when it turns back on it's slow as hell. It did it last night and the lag wasn't too noticeable but it did it again tonight and it has been lagging a lot. Any ideas what it could be or what I can do to fix it?