Hi Ilsa I get that very occasionally, I suspect it's likely just the exertion, but definitely worth varying what you eat and seeing if that makes a difference. Your body may just adapt with time anyway.
Same here as with Trinity. Last Sunday I ran a half-marathon and for the next 7 hours I felt really sick.
On training runs that never happens (except for the first few minutes after very intense reps) and when racing it's mostly when doing half-marathons or 800m races (how odd now I mention it... probably the huge build of lactic acid in the 800s).
What causes this in the half-marathons? I have heard of dehidration, heat, humidity... I don't know...