What triggers hybernation?

[dannyc]

I have a w/c black rat snake that has always eaten great for 2 months I've had it. Recently I fed it 2 rat fuzzies and he sucked them down like he was starving. About 2 hours later I noticed he had regurgitated them both back up. I waited 3 days and offered it another 1 but he wouldn't eat. Hes been about 10 days now and hasn't eaten. He may be in a shed cycle but not sure. I was wondering if maybe it just knew it was fall and was getting ready to hybernate. Does temp or light trigger the hybernation? The temps have been the same the whole time.