I’m not sure that everyone can exercise control over it. Perhaps for some people who have a specific phobia to blood or needles, they could do some kind of ther

I’m not sure that everyone can exercise control over it. Perhaps for some people who have a specific phobia to blood or needles, they could do some kind of therapy that helps reduce their fear response. I know from my own personal experience that I don’t usually vasovagal in response to blood and needles or any kind of fear, but about 2 to 3 years ago, I did a stint where I would scrub assist in some surgeries, and even though I loved scrubbing in, I would sometimes vasovagal during a procedure. Some of the tips I was taught to avoid a vasovagal in those circumstances was to wear compression stockings, eat a decent breakfast, drink plenty of water before scrubbing, and while standing still for ages wiggle my toes, and flex my leg muscles etc and things like that - and failing all those things, I learned that as soon as I lost my hearing, I needed to immediately sit down, because for some reason, I lose my hearing before I properly pass out. I know it’s kind of different circumstances but I do think some of those tips do help. Particularly having a decent meal and being well hydrated before having blood collected will probably be the most helpful, though there is no guarantee that this will work.