About 12 years ago I got Guillan-Barre Syndrome. It is an auto-immune disorder that attacks the nerves. It is not contagious at all, just happens to some people. The cause is uncertain but it was speculated that immunization shots might be a possible cause. They rev-up the immune system and the immune system attacks things you do not want attacked.
I did not have a vaccination for years after that. Indeed, when I went for one once they handed me a sheet with two questions. I forget what question #2 was but the first was something like, “Have you ever had Guillan-Barre Syndrome?” I checked yes and they noped me right out of the room.
I am not opposed to vaccines at all. I WANT to get vaccinated. But I need to be careful. I did do COVID vaccines because those seemed important to get more than my yearly flu vaccine and I have not had a problem with those. I still avoid yearly flu vaccines though.
ETA: To be clear, it is not proven that vaccines cause Guillan-Barre Syndrome…it was mostly a guess and does not mean you should not get vaccinated (the syndrome is pretty rare). It does mean, for those who have had it, to be careful about vaccines in the future since they know they might be affected. Still best guesses though.