when you lose weight fast that can happen, your bp drops suddenely at times. Be careful getting up, do it slowly if you feel dizzy.

You need to get your blood sugar tested. You may have low blood sugar and that will make you faint or pass out.

I had the same thing happen to me, my BP went 70/40 sitting and when I stood up it went to 60/50. Doc took me off both BP meds, I have more energy and haven't had the issue since.

Sounds like not enough water and protein. Get some Gatarade and get protein in. Greek yogurt has a tone of protein. Also, you really have to take vitamins. I got all of mine chewable, and in the morning, I put them in very hot water and stir them until they melt, then I sip it. I'm not a vitamin person before, but the way they made me feel better was amazing.
If you can't drink enough you will dehidrate. Get ts stuff going and I promise you will start feeling better.
Take care,
Lisa

I think you should contact our doctor. If you are on blood pressure medication it may need to be adjusted based on your weight loss. You at least need to find out what's causing the problem. You don't want to cause an injury to yourself while your body is still healing from surgery by falling.

Have your potassium checked. I was having the same problems and just generally felt crappy...had blood work done and my potassium was super low. I now take prescription strength potassium 3X per week....feel amazing now!