Two for me. Blood and ropes.
As a teenager I went to a blood donor session, not to donate but to watch. Was fascinating to see cannulas going in and blood coming out, but eventually I started to feel iffy, culminating in crawling out of the building on all fours feeling very nauseous.
To this day I'm mystified at the experience - how can I be fascinated to watch something, NOT be disgusted, yet still be nauseated? Brain needs a rewire maybe.
These days it's more a white coat syndrome. I don't often have a strong reaction but I have had one full blown vasovagal syncope following a holiday jab. Woke up to find a nurse putting a BP cuff on my arm. Can't remember how low the reading was, but the nurse sprinted out of the room to fetch a GP.
(Which is a lot better than the usual 3 weeks to get an appt).
The ropes phobia is just a variation of heights. I can climb to the top of a climbing wall no problem, but ask me to abseil down and I have the biggest problem letting go : I'm phobic about trusting the safety rope & harness. Every few years I give it a go again, either a climbing wall, a Go Ape, or a zip wire; I'm trying to conquer my fears, but in over 3 decades of trying it's not getting much easier.