Friend has odd condition

So i have a VERY dear friend of mine who is suffering from something doctors cannot figure out :S It only started happpening last year, this random pain near the back of this persons head has been throbbing for quite some time now, it pulses in with pain and it randomly gets worse, this person has fainted, blacked out at random moments, when she never has before. She has done alot of tests, blood tests eeg's ecg's cat scans and so much more but no ones seems to be able to find anything. Then, one time she went to the hospital because the pain got to an excruciating level, the doctors didn't know what it was ,but he said it MIGHT be a tumor. I am really hoping such a faith is not her path, and if so, I hope it is not a pre-malignant/malignant tumor. I was wondering if ANYONE that has heard or seen this before can probably give me a diagnosis of what it is OR any suggestions and what it COULD be, I would really appreciate this.