@JW667,
Ah, I get vasovagal responses, too.
They're eh ... fun. Not.
So! A few things I do. I try to stay hydrated, as in more hydrated than I probably need to be. Yes, I know where every bathroom is, or at least it seems that way.
I try to keep my temperature not too hot, particularly when exercising. I also can get red-faced when I work out so this helps to control that.
I think blood sugar is related to this, at least a bit. I snack during the day, not too much. Even a few grapes or almonds can help.
Overstimulus also seems to be related to it. We got out of an exciting basketball game once and I just had to sit somewhere, where there weren't a lot of sounds and flashing lights.
Finally, I also keep a cel phone with me when I run. Hey, you never know. And I have a RoadID on my sneakers. That way, in the event that I do pass out (I haven't but it does worry me a bit), at least someone can call 911 and the RoadID has my doctor's info and a way to contact my husband.
I am 51, and I'm overweight. I suppose those things aren't factors but I did want to let you know, in case you wonder if they are, they just might not be (age and weight).