I was messing in Half-Life 2 today, and I've noticed a significant drop in my computers performance. At one point, a grenade blew up and sent a few physics props flying, which should have been more than easy to cope with, but my frames dropped to 30. An other time, I was looking down the tunnel at the very end of the Ravenholm maps and the FPS dropped to 24 for about 5 seconds, then rose back to ~90. I used to be able to minamize and restore HL2 in 6 seconds, but that's up to 14 seconds (I know that's asking for a lot, but double the time is a little disconcerting).
I've made sure no other background programs are running, save for Opera, and looked in the Task Manager to see that no high-cost programs are running - I found nothing.
Can there be any explanation for this sudden loss in performance? I'm quite certain that the pressure being put on my system is far less than what would cause what I'm describing...