Should I Be Concerned About Dizziness Upon Standing, Fluctuating Pulse Rates, Chest Tightness, Shortness Of Breath, And Nausea?

Im 39 5 7 , 160lbs, I was 200lbs but stopped citalopram 2 years ago, and have lost weight i think because I stopped that medication. Three weeks ago I started feeling nausea, constipated and sick everytime I ate with lots of hiccups, and burping. I feel abit better from that now, but I don t eat much at all anymore. My doctor says its because he thinks I have IBS. Now for the past week im getting very dizzy after standing up, that i have to hold onto something for 5 to 10 seconds. So i have checked my blood pressure 110/75 or so, but my pulse was 110. So periodically during the day over the weekend when im sitting and relaxed. i checked it and its usually between 100 -120, but a few times it was 140-170. It has gone down to 80 at times. I have felt some tightness in my chest off and on, and somtimes feel short of breath for no reason. I had blood work done. High lymphocytes/ nutraphils, low iron, normal red blood cells, normal thyroid, and everything else normal except my vitamin D is double over the maximum range. I had an ECG with dopler about 4 years ago that said insignificant regurgitation on all the valves, then another ECG to years ago that said normal, and the one I just had said borderline T abnormalities, inferior leads. My doctor has no concerns that anything is wrong.