Generally, when you have what you call dreamless sleep, it is one of two things; either you do not remember what you dreamt of or you fell into absolute unconsciousness which is almost death-a taste of death. But, there is the possibility of a sleep in which you enter into an absolute silence, immortality and peace in all parts of your being and your Consciousness merges into Satchidananda. You can hardly call it sleep, for there is perfect "awareness." In that condition, you can remain for a few minutes or hours or days; but, these few minutes give you more rest and refreshment than hours of ordinary sleep. You cannot have it by chance. It requires a long training.
Samadhi is not a stone-like inert state as many people imagine. A life in the spirit (Atman or Divine) is not annihilation. When the self is bound down to its empirical accidents, its activities are not fully exercised and, when the limitations of the empirical existence are transcended, the universal life is intensified and you have enrichment of Self. You will have a rich inner life. You will have an expanded cosmic life and supra-cosmic life, too.
Excerpted from Mind: Its Mysteries and Control by Sri Swami Sivananda, A Divine Life Society publication; First Edition: 1946.