Overeating may be the culprit but in that case quite often the PC frozen completly.
Could be a lot of other things, for instance, a memory leak.
Did the hard disk spins a lot during the event??
One program assigns memory and doesn't release it and slowly "eats up" all the memory until the level of swapping became intolerable.
It doesn't matters if you have a lot of memory, it just take longer that way..
It happens when one program is running (even in background, without your knowledge) for a long time. It is solves by a reboot that cleared the memory.
Other possibilities are drivers for hardware or network using all cpu power because the respawn themselves a zillion times.
If is occurs again, try to find some info about what the pc was doing (systematic problem with this program or after using my USB camera, or whatever I do after 25.5 hours), was cpu idle or at 100%, hard disk idle or turning like crazy....
It can take forever to find the real responsible, in the mean time, labelled it as glitch (=Gremlins Looking Into The Computer Housing) or cosmic rays interference, your choice
