Help, This horse has Narcolepsy!?

so i just started riding this horse for a friend. He is a real sweetheart. Big 17 hand gelding, mostly appy but i think he has some throughbred in him. We i was told before i started riding him that he has like narcolepsy, and today he showed it to me for the first time. I was saddling him in the cross ties and he was doing great. He started to look sleepy so i started pushing his head around and talking to him and then he went down. he laid on the floor for a few minutes - i quick released the cross ties - and let him lay, he then popped up...stood there for a moment, he swayed again so i loosed the saddle and then he was totally fine. got on him and rode him for about an hour and had no trouble - except for being a bit excitable - i dont know what to do with him. He always does it when being cinched. Anyone have any ideas as to what to do?! Im at a loss, but he is starting to scare the little kids that ride at the barn!