Would there be space, or would the walls squeeze in? Would there be air? If so, how long could you breathe it? Would your skin start to dissolve? If so, how quickly does it progress? Is it possible to escape, either out the mouth or by burrowing through flesh? What sort of equipment could you bring/wear that would lengthen your survival within the whale?

Inasmuch as the answers depend on the whale's species, assume the most lenient answer possible (biggest, weakest stomach acid, etc).