So I'm collecting surface samples, and flying up to a 2.5m cargo bay to stick them in experiment containers. I sometimes have some trouble with my aim but the kerbal seems to fit inside just fine. This time when I hop out of the can, my kerbal is invisible. Weird. I can still see the RCS jets, though, so I exit and use them to help me fly to the other side of the can. Now EVERYTHING disappears! What? My altitude is red zeroes and my speed is "NaNm/s". I can swap views to the flag, but not to my ship. After a while my speed becomes "only" 37,000+ m/s and I gain altitude to match ... but I cannot go to the tracking station "while on the surface". OK. Reload a quicksave, and my kerbal is back where he's supposed to be, but day has turned to night somehow. Map view. Maybe it's because there's no sun? Also the Mun is gone now even though I was just standing on it. KSP crashes.
Restart the program while sweating bullets. Everything is back! Phew. By Kraken standards, how bad was this one?