I don't know, but wanted to say I've had similar problems this summer (heart racing, feeling like I'm going to black out, for me I get nauseous, the world seems very far away, I hear dh talking from very far away, everything gets dark, I fall to my knees or grab something for support, and then it all snaps back) My dr theorized that it might be from lack of calories (I'm still on my freaky mostly liquid diet. But all in all I feel better, I think) I've been thinking I should go back in and get my thyroid checked.