When I stand up sometimes, usually when I m tired or hungry but sometimes just randomly, I see dark spots around the edge of my vision , sometimes they close in until I can t see. When they do, my legs feel really weak and I can barely stand. It usually last five or six seconds, sometimes more. I m also really thirsty often. I can drink enough water that my stomach hurts but my mouth feels really dry. I ve gotten tested for diabetes and I don t have it.