The mind knows that the body entity persists and reappears after sleep. Whereas the mind is not sure of reappearance after the so-called death and dreads it.

Devotee:  Fear is consequent on the possibility of non-existence. It pertains to the body. One is not aware of the body in sleep. One is not afraid of, but courts sleep, whereas one dreads death. Why is this difference between the two outlooks?

Ramana Maharishi:  Desire of sleep or fear of death are when the mind is active and not in the respective states themselves. The mind knows that the body entity persists and reappears after sleep. Therefore sleep is not attended with fear but the pleasure of non-bodily existence is sought. Whereas the mind is not sure of reappearance after the so-called death and dreads it.