But these are not in the wild. they do not hiberbate in captivity. They will dry out in the airing cupboard - they do need to be kept warm, but they need moisture - spray them with warm water and within minutes you will find that the skint hat has formed over their shell opening (like the dried 'honesty' flowers) will come away and they will come back to life. You can even let them sit in a shallow bowl of warm water. Wash their shells very gently and give their soil a rake up and spray that too.
Give them a shallow dish of water, and also spray round the walls of their tank and make sure you wash their lettuce which will give them plenty of moisture.
If you keep their soil shallow, only about 1 inch all over, they will not bury in it.