Thank you for responding to the forum, sharing your story, and providing (what little there is) the most recent studies on OTS. I saw all my symptoms and similar mental anguish in your blog posts.
I hope that even the healthy athletes on this forum read your blog posts, so they have the ability to recognize the symptoms in case a training partner is showing signs of OTS .
Not sure if you hard read this previous thread, if not it’s a good one with lots of information.
https://forum.slowtwitch.com/forum/?post=3918396
Here is another link to exercise induced insomnia. Many of the contributors including me have the common link of overtraining
https://patient.info/...22168?page=4#3277187.
I was in your exact position seven years ago and after two visits to Sports dr’s who specialize in OT syndrome, I am still in a position where any exercise that causes my HR to exceed about 115 bpm, causes hellacious insomnia. At this point I really feel that the HPA axis gets somehow permanently broken and the body overacts to any sign of stress by releasing excess amounts of cortisol/ adrenaline.
Hope these links shed a little more light for you.
I’ve seen what you are describing and suffering from in way too many athletes in the triathlon community. Triathlon, in general, has an overtraining problem.
In regards to your specific symptoms, the low vitamin D is from the high cortisol. And it’s not something that supplements or sunshine will fix. You just need rest, good nutrition and learn how to relax. The Low T is probably a combination of your age, the amounts and amount of time you’ve been training, nutrition and your body just shutting it all down.
The GI issues I’ve typically seen are when athletes have pushed way beyond the limits and ignored everything their brain/body was telling them. There’s more and more research being done on how as little as 2 hours of aerobic activity can damage the gut.
I’d say in general, it didn’t take you a month to develop these issues (20 years of continuous training/racing), you aren’t going to recover in a month. And not to be the “Debbie downer†but I’ve seen some athletes never recover or get back to full health. Learning to meditate can be helpful.
I would keep working closely with your doctor and don’t be afraid to push the doctor to dig deeper or recommend another specialist who can.
Hope this helps,
Tim
competitive swimmers will rarely just go ‘swim lengths’ (at high intensity, with no specific purpose)
Ha! My perception of elite swimming is just one of endless hours of laps. 
You might be right about sprinters. But my perception of elite road cycling sprinters is they have quite a bit of trouble with over-training - at least proportionally similar to any other cyclist. Completely unscientific observation, though.
I am a lifelong cyclist, runner and sometimes swimmer.
But gave up running about 10 years ago, I am 64 years old.
I was diagnosed with Addison’s Disease (adrenal insufficiency) about 20 years after ending up in the hospital due to severe fatigue.
Shortly after that I was diagnosed with hypo-thyroidism. I take hormone replacement for both of those.
It took me about 2 years to recover from that, but then I started to do a lot of cycling and running and felt great for a few years.
In fact I was doing +100 mile rides with a lot of climbing and felt great.
But then I had sudden onset of fatigue. It came quickly without much warning other than sore muscles and lack of recovery.
I also had insomina and anxiety. I went back to my doctors and they ran all kinds of tests, but nothing explained the sudden fatigue.
I had to completely stop exercising for about six months and gradually started over again, but after about a year of gradually increasing my exercise it would happen all over again.
I went through this cycle numerous times, sometimes it was severe and other times it was more mild.
I never found a medical reason for it despite many doctors and tests.
I finally came to the conclusion that if I kept on that path it could eventually kill or cripple me.
So I decided to seriously moderate my exercise and that has helped a great deal.
Being a competitive person it has been and still is difficult, but I am convinced I made the right choice.
You should pursue all options to find the cause of your symptoms, but also consider making adjustments to your training to reduce the chance of a relapse.
Overtraining can be serious and damaging to your physical and mental health.
Good Luck.