Answer: The important distinguishing features are that in unconsciousness breathing and the breathing of the heart are both present; in death both will have stopped.
An unconscious cat can resemble a dead animal in that there may be no movement for a long period, and during this time it may not respond to such stimuli as a noise or pinching. In both conditions, the muscles relax, i.e. become limp, and relaxation of the sphincters of the bladder and anus may permit urine and motion to be passed. Bear in mind that in death the eyes do not close automatically; they may remain open just as they might in unconsciousness, to this cannot be used as a distinguishing signs.
However, two signs are characteristic of the death. Firstly, the body will gradually become colder (how cold depends on the temperature of the surrounding), and within three to seven hours the muscles become rigid (rigor mortis) a sure sign of death.
