I went through a short phase back when I was around 40 where I was becoming a hypochondiac. Every body sensation was a symptom, and usually a symptom of the worst illness possible. On a rational level I knew there was nothing wrong with me, but I just couldn't break out of the thought cycle. It was frustrating to know I was not sick, but to worry that I was. That was all long ago and far away now, but it was a rough journey.