I seem to remember this being in the book "The Sphere", though I might be wrong. I actually always thought that it was something rarely-used-but-possible.
The overlap between close-to-current sci-fi and real life in my brain is occasionally saddening/shameful.
Although I am wearing a scifi hat, not reality, assuming they don't need to breathe in hibernation, the full fluid immersion is probably a good way to regulate internal body temperature.
This is why I posted the link. I never realized the liquid was real and that the scene was shot using it. After watching the scene I thought, did they drown that rat? Effects were good, but not that good!