When I Tilt My Head Back And Look Up, At

When I tilt my head back and look up, at the ceiling for example, I begin to feel faint after a few seconds. Not dizzy, but I begin to black out. It doesn't happen every time I look up, but more often than not. I find it difficult to change a light bulb because I have to stop and look back down to regain my senses. No other symptoms.