I have had this problem for years and never knew that it was a symptom of adrenal failure. Back about 1 year ago now. I had the tilt table test that also test for this. That if you pass out then your have vaso-depressory syncope. The symptoms of that for me was that My blood pressure would drop as I stood that and I would black out. I knew there was a reason that this was happening and all any dr. could tell me was oh you just need to increase your salt. The only reason they told me that was b/c it increases Blood pressure and when it increases blood pressure it makes it harder for your blood pressure to drop enough that you will pass out. Needless to say I am glad I found that information on here. I thank you for posting it.