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Deep sleep is not nothing.
If it was nothing, we would not be speaking of it and there would be no word for it.
We know deep sleep is not nothing.
We also know deep sleep is absent of mind (no thoughts, no body sensations, no perceptions).
Could be thus be open to the contemplation that deep sleep is pure knowingness?
Consciousness ‘knowing’ itself in the absence of form.

Mike Y:  I don’t think deep sleep is absent from mind. For example you can perceive an alarm clock to wake up.

Magdi: Mike, In deep sleep there is no mind (thoughts, perceptions, bodily sensations), but awareness must be there to (at least) register the absence if mind during deep sleep , and … To hear the alarm when the alarm goes off. It is not mind that heard the alarm. It is awareness (consciousness) that does.

Deep sleep is consciousness in the absence of form. Waking state is consciousness in presence of form. It is all consciousness knowing itself as itself or as form. When consciousness knows itself as form, in fact it is choosing to forget itself.
Thus you could say that in the absence of form, consciousness knows itself as causeless peace and happiness, while in the presence of form, consciousness forgets itself and chooses to be a separate limited self.