Black out with severa headache

This discussion is related to Low blood pressure-black outs!.


I am asking this question in Heart Disease section, it can be related under nervous system.
My girlfriend, 23 years of age,  has low blood pressure and fall dizzy sometimes, also blacks out sometime but she comes back into conciousnes in short period of time. When that happens she eats chocolate or coca cola, and that helps sometimes.
Also, she has some problem with her nerve on the lower back of her head. Thats because accidental overdose of medication by doctor when she was child. The medication was so over the limit that she always felt dizzy when she was taking the medicines. Now, she thinks there is some problem with her nerver on the back of the head, it hurts so bad-she claims. Sometimes in the middle of the night, she wakes up shouting with severe pain and often blacks out. She holds whatever she reaches before blacking out, she has also hold my arm so tight that her nail pierced my skin. And after some time, she recovers and becomes normal.
This worries me a lot.
I have mentioned two kinds of black out with my girlfriend, one most probably low blood pressure, there is no pain in this black out-just the dizziness. The other one is with severe pain on her head, she cries before blacking out because of extreme pain.
I would be grateful if anyone gives me suggestion, what this might be and what can be done to prevent it. I feel this is a serious problem with my girlfriend.
Thanks