Deep sleep is only the state of non-duality. Can the difference between the individual and Universal souls persist there? Sleep implies forgetfulness of all differences: This alone constitutes happiness. See how carefully people prepare their beds to gain that happiness. Soft cushions, pillows and all the rest are meant to induce sound sleep,that is to say to end wakefulness.
And yet the soft bed, etc., are of no use in the state of deep sleep itself. The implication is that all efforts are meant only to end ignorance. They have no use after realisation.
Source: Talks With Ramana Maharshi Book
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