One of my friends who has a particular medical condition was on some FB groups for a while and she finally realized that this was not beneficial to her because people who had the same diagnosis on one hand may or may not have some of the actual physical manifestations through life that she had experienced, and she was seeing all these horror stories of this that or the other which could go wrong and yet she was doing just fine mostly when it came to the physical stuff....it finally clicked that this was not healthy for her to keep reading about other people's experiences which might be vastly different from her own in so many ways, and she quit all of those groups.
My own experience was similar in that I was involved in a couple of FB groups related to the syndrome with which I was born, Treacher Collins Syndrome, and after a while realized that this was not at all helpful to me to keep reading about others' experiences, especially new parents' where it was all rehashed time and time again..... I decided that I didn't need to be reminded on a daily basis of my syndrome and that in many ways it was far healthier to move on past that and live my life as I had been -- taking it into account but also doing my own thing in spite of it or working with it. Early on, though, in the very beginning before there was even a FB thing at all some of us, especially adults with TCS, did make a connection through first an email "loop" and later a Yahoo group and that really was valuable in a lot of ways.
The other example which I can offer as being more harmful than useful and helpful is that of groups focused around eating disorders, as for me when I was really in the midst of it, those web-based online forum groups felt essential and supportive, but only later as time went on and I made a gradual shift in my own thinking and behaviors did I realize that actually, this really was not the way in which I wanted to continue living my life and I stopped visiting/reading those forums. This was years ago, when the whole "thinspiration" thing was getting underway on some sites while on others recovery and a different approach to one's life were emphasized. I saw both of them as they were developing and happening. I have no idea of what kinds of groups related to eating disorders are on FB because I've moved past that whole thing now.
To repeat: the internet and web-based discussion forums and FB groups around specific physical and medical issues are not in any way a reliable source for actual in-person medical advice and treatment.
