daughter who passes out

I have a 22 yr old daughter who passes out every so often, she has had work ups done on heart, adrenal glands, etc. The only thing the doctors can tell us is her blood pressure drops from lack of fluid. She drinks alot of water, and coffee,some alcohol at times, She used to get this in the am and have orange juice and it would help, now it happens even during day and at night, she always eats throughout the day, protein and salt to help with the fluid. She'll start to get dizzy upon rising and breaks out in a cold sweat, turns white and doesn;t have much time to think about it or sit down and she falls, has hit her head and chin because of this. Last night she passed out even when she was sitting this is the first time that has happened. She has very fine thin hair and worries about balding, very oily skin and skin breaks out easily. Anyone have any ideas or have heard of this I would appreciate any help, she also sweats a great deal especially her feet, Thank you