I think it's unfortunate when people ignore the possibility of psychosomatic symptoms, but even more dangerous when they attribute every issue to it. It should be a tool in the toolbox, a possible explanation/approach to ailments that are sometimes simple and singular but often times complex and multi-faceted.

My N=1:

I have chronic back issues. At best it's general tightness and fatigue, but can also be sore and painful. In particular I had two incidents in 2011 (in a matter of seconds) and 2012 (over a couple days) where my back spasmed and left me crippled, unable to move without knife-stabbing pains and unable walk down hallways without holding onto a wall. Both lasted almost a month, and were followed by months of heightened soreness.

I was 23/24 at the time, with no preexisting health issues. I'm a regular runner and in great health otherwise. I tried to fix this with deep tissue massage and core/strengthening regimens, and largely those helped keep the pain levels down but really only halved the symptoms at best. A friend had been recommending Sarno's 'A Divided Mind' which is all about the psychosomatic diagnosis since the first incident, but I had dismissed it. Finally in 2013, as I felt a new round of the spasms coming, I gave it a shot. Lo and behold, it became the single most effective tool I've found to manage my back issues. I identified that each spasm came with a major emotionally loaded event. In 2011 it was unrealistic pressure to compete at a big running race I had been training for. In 2012 it was participating in the search and rescue for a dear friend who was lost (and died) in the wilderness. In 2013 it was a nasty falling out with my best friend (and brother) at the time.

I don't believe the mechanisms are fully understood, and I think Sarno in particular does too much hand waving. But using his approach was the first time in years that I had no discernible back issues. I liken it to getting butterflies in your stomach. Your mind and emotions can trigger physiological changes to blood vessels, nerves, muscles, etc. that in turn can cause real issues. I also don't believe it's the only factor. I started an office job in 2015, and back issues have come back that I attribute 100% to the office lifestyle. I've found no relief with the psychosomatic approach, but do better with a sit/stand desk, breaks, and daily exercise.

Overall, I think a ton of people could benefit from approaching health issues from a psychosomatic perspective as one of many possible diagnoses. I also agree there are so many other possibilities that assuming it is always in your head is ignorant, neglectful, and downright dangerous.