My feet were a little swolen, even the next day. No stomach sloshing, though. Yep, I got a little lightheaded at first, like a “stood-up-too-fast” headrush that got progressively worse until the black curtain came down. I don’t think I was sitting for more than five minutes or so.
In my mind, the blisters were a root cause of the whole problem. Were it not for them, I would have had no reason to stop, or to stop running for that matter. I need to talk to my running shoe store and see what they have to say about possible fit/sock/gait issues.
OK, so your stomach was emptying (no sloshing) - some people drink so much their body just can’t absorb it.
However, the swollen feet are a clue that you may have still overhydrated. I’m armchair quarterbacking a bit here, but swollen feet may have placed extra pressure against your shoes and caused blisters where you have never experienced them before. Then when you stop to fix the blisters, the blood pools in your legs, you get lightheaded, and presto - blackout.
Did you drink more per hour in this event than you did in training? That can be easy to do when they keep handing you bottles and cups out there.