Negative tilt test but bp dropped 71/54 after stress test at about 18 min recovery sitting down. hr was still at 110. hands tingling,lightheaded

Your signs and: symptoms are most consistent with dehydration. Although you may have autonomic dysfunction it is more likely to be simple dehydration. Tilt table testing has a moderately low sensitivity and specificity. 57% and 83% respectively. A negative test is not definitive. Treatment is pretty much the same regardless so eat more salt and hydrate more rigorously and see if you get better clinically.