I have not had to deal with overdraining, however, my understanding, is that if the shunt is functioning properly the ventricles should reduce to their proper size. Ventricles enlarge due to the pressure and fluid build up. I believe that unfortunately if he has a spinal tap and/or has an opthamologist look in his eyes. I have had 5 headaches in my life and wouldn't wish them on anyone, they make migraines look like a bump on the head, generally the best place to be is in a dark room with your eyes shut, however, the issue there is when the shunt is not functioning correctly it can lead to Vertigo, which means it doesn't matter if you're standing, sitting or lying down. Five headaches, five surgeries no issues.