I have the exact same problem (also temporary darkened vision) when I stay at a very high excretion level and/or heart rate for an extended period of time, or I stop too fast without an adequate cool down (it comes on stronger and faster immediately after hard running or hard lifting than cycling).

I’ve found that when it comes on the worst, I’m not well hydrated or was lax on nutrition earlier in the day.. and was essentially running on empty.

However, even when I’ve taken extra care to make sure I eat well and hydrate, my body quickly jumps to that “vomit zone” if I overexert myself and accidentally get my heart rate and breathing up too high.