What can cause shortness of breath? x-ray, ct w/contrast, echocardiogram, holter monitor, stress test all normal. still get feelings of elephant on lungs at random sometimes lasting for hours. finger o2 oximeter reads 99-100?

In my experience shortness of breath caused by anxiety is noted more at rest than during physical activities perhaps because the individual is distracted during those times. Your tests indicate normal heart status. Although you haven't had pulmonary function testing, I expect no pulmonary pathology either. Stress management therapy would help if you think you're a candidate.