This is just a classic case of phone in need of flashing and how it cures things. Whenever your phone starts acting really weird, it's time to flash, and that will cure everything in 99 44/100% of the cases.

It is probably just a case of some corrupt files that occurred when you crashed, due possibly to undervolting, exactly the risk that you take. But since flashing is so easy and normally so successful, it's a risk worth taking -- but if this had happened to me, I wouldn't go back to the starving setting without some hesitation (thought I still might go back to starving anyway, just to confirm whether or not it is really the problem).

No need to beat yourself up about stupidly not reacting to overheading. The N900 is a fantastic device to test with and recovers from almost everything beautifully.