Hey,
My mom has these headaches for 2 years now.She had a acoustic neuroma 2 years ago it was successfully removed but about 2 days after she developed these headaches. Its like tense headaches, could last from 30 seconds to few hours. Also she has said that when she lies down the headache gets better. Headache itself is at the back of the head on right side, palce where she had the surgery. She has visited 3 neurologist but they don't know what cause it. Surgeon who performed the surgery said that surgery went fine and it's not from that. One doctor said that its from tension. She have tried acupuncture, massage and visited chiropractic. Over the 2 years her headache has toned down a bit, but still has bad days.