What should you do? Ring your parents to organise a funeral, you probably only have a few more hours to live. Hamsters are known to chew upwards when put into tight situations, it's highly likely that you may find it hard to breath or poo sooner or later (not just because there is a hamster up your backside, but because it has chewed your internal organs). It will more than likely come out of the mouth, if it is able to make it's way, otherwise you may feel extream discomfort as it knaws through your skin to get out.

Good look, and may you rest in peace.