Chandogya Upanishad 6.15

'If a man is ill, his relatives assemble round him and ask: "Dost thou know me? Dost thou know me?" Now as long as his speech is not merged in his mind, his mind in breath, breath in heat (fire), heat in the Highest Being (devatâ), he knows them.

'But when his speech is merged in his mind, his mind in breath, breath in heat (fire), heat in the Highest Being, then he knows them not. 'That which is the subtile essence, in it all that exists has its self. It is the True. It is the Self, and thou, O Svetaketu, art it.' 'Please, Sir, inform me still more,' said the son. 'Be it so, my child,' the father replied.