It is true that deep meditation induces a kind of absent-mindedness as attention gets more and more withdrawn from the external world. It is as if a part of the person were not present, and indeed, this is what happens. There is a partial, if temporary, loss of ordinary self-consciousness of some part of the I and of the senses. At this stage of meditation he should let go of what he knows and let the Unknown speak to him.
-- Notebooks Category 4: Elementary Meditation > Chapter 1: Preparatory > # 252