Doesn't he need to go into the Odinsleep once a year or something like that? Why is it treated as sort of a big deal/like he's dead when he enters it?
It looks like they all sleep normally, but Odin is so old that much like the Goa'uld he needs something more from time to time, perhaps increasing in frequency as he ages, like the sarcophogi.
In the film it looked like a weak forcefield, maintaining a type of life support/artificial environment for him, but the FG's state that he is technically "aware" of everything around him, even able to hear whats happening, just immobalised by the field.