Sentence:  Very quickly it would come to seem to Lionel Hoffmann that the remainder of his life, all that was not Siri, was of little more substance than those <WSD>hypnagogic</WSD> images that flash against our eyelids when, in a state of exhaustion, we begin to sink into sleep. 
Meaning of the word marked with <WSD> tags:  That accompanies falling asleep; especially, pertaining to the semi-conscious period immediately preceding sleep.