Just as Dr Diana said you will see the BP go up instead of down. I was dx many years ago at Mayo ( not my favorite place) and had the exact test she describes above. My catecholamines were off the chart when drawn after 30 minutes of lying flat in a dark room and upon tilt ( off meds for 2 weeks)here is what i got- Resting lying flat HR 78, BP 132/78—upright 1 minute HR 102, BP 154/96, upright 3 minutes HR 124, BP 188/108 Upright 5 minutes HR 148 BP 204/122. Test discontinued at that point by autonomic doctor. Although I am much more controlled now with beta blockers I still fail the tilt with my HR.