I have no connection with this kk monster that you all speak of all over this forum. Please refrain from suggesting that I do, as from what I gather she gets banned every day.
You'd think they'd have cottoned onto her killing people with hails of arrows or turning them to stoner with her stare, And dont get me started about her snakes for hair and poisonous acid for blood. I mean seriously how hard can it be?
I find that any really intense run, (marath0n, half marathon, time trial) can make me feel rubbish and can lead to some combination of soreness, fatigue, digestive distress, headache, nausea and so on. It varies.
There are some aspects of recovering from a hard effort which remind me a lot of recovering from a hangover, in fact. I'm sure I'm not the only one
Also your stomach can only take so much water before it cant put it into your gut to go towards hydrating you and the rest just sloshes in your stomach. Neck enough fluid and Run hard like that and your body may well say 'enough is enough' and eject it all.
Really there are plenty of possible causes here - you should really experiment during your longer weekend runs and then settle on whatever formula works for you. Certainly don't try anything new on race day when you are sensitive to everything.