I'm not exactly sure what they do either except what Lilysmommy has mentioned.
When in hibernation, their organs start to shut down. Numerous years ago, there were a couple of hedgehogs who were in hibernation for a couple of days. One ended up dieing fairly soon despite vet care and the other survived for a while. I'm not sure if this it was posted on here or CnQ. It was quite a few years ago so I suspect if it was here, it was in the old forum archives which I don't think are accessible any more.
* * * Nancy * * *
Retired from breeding
Rescue contact for both the Hedgehog Welfare Society and the IHA
Rescued over 70 (and counting) hedgehogs needing a new home