Sentence:  A `` mental image '' subconsciously impressing us from beneath its language symbols in wakeful thought , or consciously in light <WSD>sleep</WSD> , is actually not an image at all but is comprised of realities , viewed not in the concurrent sensory stream , but within the depths of the fourth dimension . 
Meaning of the word marked with <WSD> tags:  a natural and periodic state of rest during which consciousness of the world is suspended