If he feels better as the day goes on... he could be under draining, i.e. if being upright helps him feel better (if he has an programmable shunt, it may need adjusting to a lower setting but he may not like the lower setting if it puts him too far down). Or he could have some mild intermittent problem, but that would hopefully be less dependent on position. Sounds like a great time for him to talk to his surgeon's office. If he feels better after sleeping with his head elevated, that might be just enough to compensate.