I really do not know about the hibernation. Perhaps the kefir is like kombucha in that the good stuff only slows down.

I like to make my own kombucha and put it under pressure to create some fizz. Most do form fizz, but some do not. When the bottle start to get fizzy, I immediately refrigerate them. A while back I had 4 that were cold and not fizzy. I wondered if I put them back out in room temperature would
they get fizzy. I set them out over night and when I checked them the next day 3 were fizzy and one had exploded from the pressure built up with the reactions creating CO2. The little fellers were mere at rest. I, too, make milk kefir and like it very cold. I figure that my body heat will stimulate the good guys/girls.

Oh, yes. I have learned that when I am trying to make the kombucha fizzy to put the bottles in a waterproof trash bag. I have had 6 or so to explode. The warmer the temperatures, higher probably of explosion.

Yep to all that. Kefir hibernates.
Wake up depends on temperature, stomach being hotter the most av daily temps. T2