I had it a few years ago and my reaction was like the worst case of flu I ever had, but it only lasted a few days. Get it because no matter what your reaction, it will be a walk in the park compared to if you get a case of shingles.
After 6 months the effectiveness of the J&J shot drops from 86% to 13%. Ask your doctor if you should get the booster.
https://www.webmd.com/vaccines/covid-19-vaccine/news/20211105/covid-vaccine-protection-drops-study