Ze has a couple like that. Uke faints during sex, another time in the rain, and I guess in a pond too. Their background story starts in chapter 13 http://www.mangago.zone/read-manga/ze/an/ze-chapter-13.html/1/
Idk if you've read the Kuroneko series but Shingo faints in his first sexual encounter with Kagami (the first chapter of the first book of the series)
There's also a series where the seme has a such a strong sex drive he keeps screwing the uke even after he faints but it happens later in the series. Not sure if you wanna read it from the start. Tbh the art isn't good but I have a soft spot for the story
Here is the series where this happens: http://www.mangago.zone/read-manga/oboreru_kemono_no_koibito/
Here is the first manga of the couple http://www.mangago.zone/read-manga/beautiful_beast/
Can someone please help me find some yaoi manga where the uke faint during sex or some accident ???