Charles Dodgson on 02/09/1856 wrote in his diary:

Query: when we are dreaming and, as often happens, have a dim consciousness of the fact and try to wake, do we not say and do things which in waking life would be insane? May we not then sometimes define insanity as the inability to distinguish which is waking and which is sleeping life? We often dream without the least suspicion of unreality: 'Sleep hath its own world,' and it is often as lifelike as the other.