Sleep is a completely inactive state of being. When a person wakes up from sleep, he or she may feel slightly refreshed but also a little sluggish, asking for a tea or a coffee to wake up completely. The person appears a little heavy and dull because sleep has a Tamasic nature and the sleeping person rests in it for a while. During sleep, the Vasanas and Samskaras are in a subtle state, and hence the slight sluggishness.
In the samadhi state, the person is in touch with the Atman within, and rests in pure awareness. In this state, the Vasananas and Samskaras are burnt by the fire of the Atman. Samadhi is a state of inner alertness where the person becomes pure consciousness. Samadhi is union with the Brahman. It is a state of eternal bliss and wisdom. Samadhi is a state that when experienced, one knows what it is like; it cannot be explained by one who has not experienced it. In Samadhi, the mind, intellect and senses, stop functioning. Samadhi is perfect self-awareness. In this state of Samadhi, the Jiva becomes one with the Atman.
For those who attain the grace of God and Guru, entering into the Samadhi state becomes very easy. Otherwise, it is extremely difficult to enter into the state of Samadhi. So, struggle hard, and with complete will-power, obtain the grace of God and Guru. When you live in seclusion, and meditate continuously, it will become easy to obtain the grace of God and Guru. When a person awakens from the state of Samadhi, there is a sense of complete wisdom and knowledge. This is the reason why Yogis who spend long hours in the Samadhi state are filled with the wisdom of Atman.
So, make it a practice to sit absolutely erect with your spine not resting against anything, perpendicular to the bottom of your seat. Then you shall find yourself alert and full of wisdom when you awaken from your meditation. You will find yourself fully composed and full of bliss. You shall then be sure that you have been in Samadhi and not in Sleep.