Has anyone else experienced this?

So, I finished an olympic duathlon on Sunday, and had an unusual physical symptom thereafter.  This has happened to me before, one time, but so far, I've found no one else who has had this.  Oddly enough, this happened the first time after the same race, one year ago.

I cross the finish line, I'm in the mode of taking water, gatorade, light food, and suddenly, my vision fades.  For the most part, I can see only bright white (that is, everything is bright white to me, regardless of it's actual color).  I can see enough contrast and just enough color to tell that I am looking at a person, or a tree or a table or what have you, but it is almost like what I imagine it is to be legally blind.  (for the record, my corrected vision is fine, and I was wearing contact lenses.  I had no problems whatsoever in the race, with respect to vision.)  this happened, went away and came back, with a big pressure-type pain behind the eyes.

I went to the medical tent, and the physicians hadn't seen anything quite like it before.  Eventually, the symptoms went away on their own, and the docs decided it was probably a combination of hypoxia and dehydration.  Dehydration seems odd to me, as I took a lot of fluids and electrolytes over the course of the event, but hypoxia is possible (as in undiagnosed asthma, or something.)  They let me go with the admonition to go to my local ER if the symptoms returned.

Anyways, I am following up with my physician, though I doubt he can tell me much as the symptoms haven't returned - it's been two whole days now.

So, I am seeking opinions, to determine whether there is a possible cause that can be investigated further.

Thanks in advance,
Scott