I had to get allergy shots when I was a kid. I hated the shots and hated needles for decades after that.
And some of the needle experiences I had just made it worse. Like the time I was getting my blood drawn to get my flight physical updated so that I could go to flight school, the nice young E-4 doing the bloodletting left the needle stuck in my arm while she went to answer the phone.
In about 1/3 of the annual flight physicals I took, I passed out after giving blood. Vesovascular (?) syncope, I think it was called.
The first time I voluntarily donated blood I was about 40, and I passed out.
Next time, I forced myself to do all the right things about keeping my hand squeezing on the little ball, etc. I conquered the beast.
Having done all that, after getting to where it does not bother me to give blood anymore, after having done so regularly for over ten years, I have recently found that I am testing positive for hepatitis (B, I think). This is probably from the gamma globulin shots we got for the disease when we entered mission cycle (every 18 weeks)in the 82nd Airborne.
I don't test positive when I get my annual check-up at the doctor's office. But the Red Cross must have started using a more sensitive test, because I now show up as having had hepatitis after giving blood to them.