Sudden hissing while hibernating

I have had my adorable Russian, Mikey, for about five years. We used to be very close and he would perk his head up when he heard my voice. Now that college is much more time consuming, I hardly get to spend any time with him. Recently he's started making a very strong hissing noise(VERY loud- it sounds awful), similar to when he pulls his head in, but his head isn't moving. His legs sometimes bob a little when he does this. He also isn't eating, and since he's almost done hibernating, he usually would. We had an uncharacteristically cold winter, so he's been sleeping with me for warmth, hoping that would solve the problem, but it hasn't. He's never acted like this before, and I'm starting to get really worried. Any suggestions?