Okay, it's back.

Nvidia driver is only 0.0.02 versions back. I'll try going into text mode and unloading the module to see if that helps.

The only additional info I've been able to collect so far is that the reported number of interrupts and context switches drops off dramatically during the pause. Still doubtful that it's anything more than just symptomatic, though.

There is absolutely zero swap activity, so that's not it.