I'm not going to tell this female friend to go see any kind of specialist before I pick the minds of getbig.  Answers here tend to be more accurate anyway 
 "I've been very dizzy lately when standing up. 4 times in the last week, I stood up and got so dizzy my vision went black, I fell to the floor and became unconscious. I wake up not knowing where I am or what's going on for a few seconds and I am sweaty. People that have seen it happen say I'm unconscious for 15-30 seconds each time. I went to the ER. My blood pressure was very low and my heart rate was so high they ordered an EKG, but it came out fine."
"I've been very dizzy lately when standing up. 4 times in the last week, I stood up and got so dizzy my vision went black, I fell to the floor and became unconscious. I wake up not knowing where I am or what's going on for a few seconds and I am sweaty. People that have seen it happen say I'm unconscious for 15-30 seconds each time. I went to the ER. My blood pressure was very low and my heart rate was so high they ordered an EKG, but it came out fine."- 30 year old female.  5 foot 3, 110 pounds.  otherwise good health, moderately active.
Any advices from getbig?   Thanks!