Have Noticed That A Good Friend Suddenly Has One Eye

Have noticed that a good friend suddenly has one eye (his left one) has started drifting noticeably to the side and not lining up with the other eye when he is looking at me. It happened several times within a hour. Can you tell me what this is usually indicative of? This is new. Once I told him what I was seeing, he did notice the same thing while he was looking in his mirror as he washed his hands.
YYYY@YYYY