I have the issue with lightheaded and dizziness when I first stand. I am about 20 months out from my surgery with 140 lbs down. When I talked to my Dr, they reduced my dosage for my heart rate and blood pressure. This has not gotten rid of it, but made it much better. From what I understand, my blood pressure was much lower than it used to be and when I would stand, my body would send blood to my legs leaving my brain a little low due to reduced pressure. After a few seconds or minute, the blood returns.