This New York Times article explains why falling and lying on the floor for several hours could become life threating for seniors.
Creatine phosphokinase, or CPK, is an enzyme found in muscle cells in the body. If a muscle is injured or inflamed, the level will rise.
That injury, called rhabdomyolysis, was first described in survivors of the London blitz in World War II who, though rescued after a limb had been crushed or pinned under fallen masonry, later died of kidney failure. A British physician, Eric Bywaters, determined that the crushed muscle cells leaked the protein myoglobin into the blood, where it was then able to poison the kidneys. He published his findings in 1941.
The level of CPK in Martha’s blood was through the roof. Though she had not been pulled from rubble, by quietly lying on her bedroom floor for so many hours after falling, her leg pinned beneath her, she risked complications as severe as those of any victim of a building collapse.