Richard’s Correspondence with No. 111,
RICHARD: [..] there has been many an occasion over the years where, in face-to-face conversation, many a person has felt overwhelmingly sleepy – complete with compulsive yawning and irresistibly heavy eyelids – despite being vitally interested and (up until then) participating keenly in what is being discussed.
Upon enquiry replies have generally been to the effect that it all just gets too much to take in at one sitting/ all at once (hence the autonomic shutdown).