What Causes Severe Pain On The Head With Giddiness In Absence Of Top Skull Bone?

My brother's son has lost his top skull bone in an accident when he was a child. Now he is 26 and recently a ball hit him on the head and he developed severe pain and was admitted to CMC. He has been given EPTOIN (Phenytoin Tablets) 2 tablets 100 mg each time, thrice a day. He has developed giddiness and vomiting subsequently. He also gets recurrent fever and headach every 1 hour or so. Is is advisable to reduce the dosage?