Alt-Tabbing while you have an foreground application producing full screen high-resolution graphics and 3D live polygon rendering, straight back to a measley 2D rendered desktop (potentially of different colour depth and resolution) can be quite a lot of stress.

And finding the culprit could be as simple as differences in resolutions, to acceleration support in the driver version.

One method I use to do to get around it was switch into a standard low-res menu or bring up the old console screen before switching out. Ensuring there was no live rendering occurring at the time. Lessens the chance of the OS swapfile etc having a sudden hernia as resource allocations change.