reason for concern?

So this morning, in the shower, I started to feel a kind of buzzing in my head, and my vision started to turn black. This has happened to me before, periodically since at least college. So I just sat down for a minute until it started to go away, and then stood back up. Then I opened my eyes again to discover I was back on the floor, stuff had been knocked off the little shelf, and the stall door had been knocked open. Not a good sign.

So, considering that I asked the doctor about this in college, and she said she couldn't find anything wrong except maybe blood pressure on the low end of the scale, is this something I need to worry about? Is it because of the weight loss? Or maybe the recent influx of caffeine (Rich has rediscovered our coffeemaker)?