In a way sleeping is sorta like being temporarily dead.
You go to sleep and your body is repairing itself and recharging itself and your body temperature lowers and you go partially unconscious when sleeping.
However when your dead your body completely shuts down and your brain shuts off completely and your heart stops.
When you're dead you're no longer conscious and cannot and will not wake up from the permanent sleep and you won't feel anything or be breathing.
Your body then starts decaying and your body goes into rigor mortis and your body becomes stiff.
Sleep is a bit like being dead but being in a Coma is more like being temporarily dead.
When you die though you won't have any thoughts or see anything or hear anything anymore.