Gordio,
Don't freak out, this happens to me just about every year. It's either hydraulic pressure from the groundwater or ice in the seam that pops the liner out. If your liner isn't too old they should be able to pop it back in once it warms up a bit. It may require you to actually drain the pool so they can put a vacuum in between the liner and frame and draw out any air, then they just pop it back in. This happened to me last year when about 1/4 of the deep end came out. If your liner is really old though it might be brittle and if that's the case it's another world of problems.
This year it looks like I only lost a foot or so in the shallow end.