Hi, I had a few experiences like this post surgery, as if I was going to pass out and had to sit down on the floor in a pharmacy for a bit. And they did happen the first few weeks after my surgery when I was out walking around the block or running errands. Usually, I feel colder now than I did before after shedding weight. I also just turned 50, so for all I know, maybe I was experiencing hot flashes, it's confusing to parse it all out. I had to really take it easy after my surgery. I would go out for a 20 minute walk and be completely wiped out the rest of the day.