I found hair to be much more useful. It told me a lot of things in addition to being fairly accurate in electrolytes, it really provides a wealth of information. Make sure to use either ARL or trace elements labs - because they don't wash the hair. Lots more about this type of thing over in the adrenal fatigue forum.
What's your diastolic BP? Hair is meaningless IMHO. Take your BP lying sitting up on your bed. Take 3 readings in both arms. Average your diastolic and then tell me what that is. If you can't do that, go to a local store that has a bp machine.
I would suspect low aldosterone then. Obviously a lab test would be needed for confirmation. How is your heart-rate when you go from supine to prone? Does it jump a substantial amount?