Back in the mid-90s, I developed a very painful inflammation in my joints and tendons that would come and go in different areas of the body. I never did get a definite diagnosis for it, but after reading about arthritis and nightshades, I decided to stop eating nightshades to see if it would help. It did help, and I noticed that eating nightshades could set off a flare-up.
The bigger picture, though, is that this inflammation started about a year after I'd started smoking again after having quit 13 years earlier. I quit smoking, and over the course of a few years, the inflammation went away completely. Nightshade veggies are no longer a problem for me. I think the condition was a reaction to the tobacco, which is also a nightshade, and I think it made me sensitive to the nightshade veggies.
These days, the only nightshades I routinely eat are tomatoes, fully ripe bell peppers, and hot peppers. I ditched potatoes along with all the other endocrine-hell-inducing starches, and I'm not drawn to eating lots of eggplant.