I had a school friend who used to hit the deck at the sight of a needle, he went on to be a phlebotomist and is now training to be the world's oldest newly qualified nurse. I don't mean to be a dick by mentioning this, just giving a story of someone who overcame this phobia. I don't know how he managed it, but I would guess that gradual familiarisation would be it. I can ask him if you're interested in the answer.
I had my first jab today (go team Pfizer...wooo!), the place you had yours sounds very well organised. When I arrived for mine, I walked past someone sat on a step looking shakey with a glass of water! The holding cell for the 15 minute cool off was dodgy too - no ventilation and the only free chair when I arrived meant that I sat well within a metre of the door and had the pleasure of subsequent injectees walking past me. I felt no compunction about being "that person" who opened the exit door with his elbow and closed it with his boot.
Until opening this thread this evening, I didn't know that a nocebo effect was a thing, but can see how it can be. Within less than a couple hours I noticed my shoulder feeling dodgy when I tried to put my hands behind my head, and then some weird sensations in that arm which have cleared up now. Fingers crossed a trick shoulder is all I cop, I hope you're bearing up by now. It's making me feel quite nostalgic for my rugby days, when I would wake up the next day feeling fine, then move a body part and realise I had a pain in it!
I tried the acclimatisation thing - I learnt, and then used dry needling (Western Acupuncture) for 6-7 years. I got to the stage where I was mostly okay (nervous, but controllable) sticking needles in other people, but still got shaky and nervous sticking them in myself (which is not a good look when you're trying to reassure someone how harmless they are by demonstrating on yourself).
I quite when A] I moved, and had to jump through a number of hoops to be allowed to continue, and B] Someone else had started in town that I could trust to refer patients to. That was 10 years ago, and I've de-acclimatised since then.
Yesterday was wierd for me - I expected my deltoid to be sore after being stabbed, but not everything from my forearm to my neck, to feel like it had taken a good rucking. A headache threatened, but never really took hold; but I just had no energy - I was expecting fatigue - like 1-2 bad nights sleep; which is normal enough for me; but... I basically stayed in bed all day, no appetite, couldn't even concentrate enough to read my book (thank gods for cricket, even if it was disappointing, and over rather quickly for a 5-day test!). A few hours after the jab I fell asleep on the sofa - which is virtually unehard of for me, then slept a good 9-10 hours which is unheard of for me; then through the day yesterday I probably got another 5-6 hours of sleep in.
Last night was much closer to normal, earlier than usual getting to sleep, but waking at my normal (dammit!) 3.30. Arm this morning is basically fine - aware of the site of injection, but only if I actually think about and test it.