That they do. I've been working through chronic fatigue for six years now, and I spent two years thinking it was somatic. No amount of meditation, therapy, socializing, antidepressants, or supplements made a dent. Thankfully I found my way to r/cfs which has fantastic advice on dealing with long-term chronic illnesses. It's a little depressing, but also freeing to accept that there truly is no cure to these horrible illnesses (there should be, but there still isn't). I'm glad I ruled out somatic symptoms so I'm sure that it's not that, but I'm also glad that I now understand that a lot of chronic fatigue is 100% biological. If I ever recover I plan to go into biochemistry to help all of these people who truly cannot be cured with today's technology.