I've had him since 2011. I just rely on room temps at night as I was advised long ago not to use a heat pad, but can easily obtain one if needed. I took him to the vet in the past 6 months and he got a clean bill of health. He has behaved like this before in the winter but not every single one...
My 10-12 year old Russian buries himself in his substrate daily. If I dont dig him out in the morning, he wont come out to eat. He usually only does this in the winter, does that mean he is trying to hibernate?