Problem:

Mammals have lungs, so do marine mammals. Nevertheless some marine mammals seem to die rather quickly when they strand on a beach.
As they have lungs and can breath while on land, why do they die so quickly? Not being in water only restricts them from food.

Question: Do they maybe try to get back into the water so rudely that they get hurt by rocks and/or break bones?

Pressure difference doesn't seem to be a problem as they can jump out of the water as well.

Justify your answer.