You should know that I passed a “poor man’s tilt table test” (what you described) when I was first ill. On the ‘real’ tilt table test, however, my heart rate went up 50 beats/minute. Sometimes the poor man’s is not indicative of POTS (some of us use our leg muscles even without trying). I would suggest a real TTT. Magnesium shouldn’t be sufficient to throw off your results. Yes, catacholamines is a blood test.