Thanks everybody who's replied so far! I wanted to share an update, since I figure the people who will benefit most from this thread are others with similar symptoms who run across it via Google, and I've learned a lot these past few days.

This is going to be long, so first, the tl,dr!

:: It was overtraining
:: Stopped doing anything that made me break a sweat
:: Eating a lot a lot
:: HMO docs worse than useless, know nothing about this and are unwilling to learn even when you do your own research and try to share it with them
:: Got a good doc who is running a number of urine/saliva adrenal stress panels to see what's misfiring (epi, norepi, cortisol, cortisone, GABA)
:: Insomnia is still the bane of my life but is relenting a bit, and pray pray pray I might be out of the sleep ICU
:: Testosterone/libido not coming back and according to the doc will take an eternity to reboot unless I take scripts, so I'm taking scripts
:: Finding that OTC adrenal stress meds (kava kava, holy basil, Seriphos) really work, especially kava, which is a godsend
:: Low dose anti-depressants for insomnia (amitriptyline, trazodone) also worked once my system cooled off

While this could still be some freakishly rare affliction like an adrenal tumor, the odds seem about 99% that I'm suffering from the Exercise Hypogonadal Male Condition (EHMC), a number of excellent papers on which by AC Hackney can be found in on the NIH website. If you're familiar with the Female Athletic Triad, you can think of EHMC as its male counterpart, with roughly the same constellation of symptoms: disruption to the endocrine system, derangement of sex hormones, and damage to the body itself (often bone depletion or a weakened immune system, among others). I was pretty sure that overtraining and undereating caused all this, but reading those papers and talking to/reading blogs by runners and cyclists sealed it - I've got the same cause, the same symptoms, and the same initial response to the suggested treatments. @lioness is on the same page as I am in suspecting adrenal dysfunction, but what I still haven't figured out is precisely what kind of adrenal dysfunction this is and how to treat it. I did find a good doctor (finally) who ordered a panel to test my diurnal cortisol, cortisone, epinephrine, and norepinephrine, along with a neuro profile, the results of which should come in this week. He's also got me on some meds (Clomid) to try to reboot my testosterone and libido, which is still abysmal but flickering back to life.

I talked to a few endurance athletes I know and read a lot of blogs and threads by guys who've overtrained themselves into oblivion, and it seems like the symptoms of male overtraining come in stages: first some strange physical reactions here and there, then emotional and hormonal dysfunction, then major disruption, physical debilitation, injury, extreme fatigue, and malaise. I was lucky enough to catch this (or get caught by it) before I got to the scariest stage, and what I've heard from everybody who's been through this is that step one is STOPPING THE TRAINING COMPLETELY. (Step two, if you eventually start training again, is never again training anywhere near as maniacally as you were.) So I quit everything but a morning walk and 20 minutes of yoga, and am otherwise going to stay glued to my couch for at least a month. (I was also on a heavily reduced training regimen for the two months before taking the hiatus, and that helped.) Here's what I've noticed so far:

* Most of the little issues have gone away. I don't wake up with calf cramps, my knees don't hurt when I walk up the stairs, and the gob of phlegm that was forever lodged in my gullet is almost gone. (That phlegm was so bad a month ago that I couldn't bend over and talk at the same time without hacking up a wad.) The irritability has cleared up too, thank God - even when I'm on very short sleep for days in a row nothing really fazes me, even major major stuff, whereas two months ago I was so jacked up and triggered that I could barely handle my cat unplugging my laptop or the car in front of me not banging a right on red. I'm my mellow self again and I couldn't be more grateful for that.

* The bigger problems have cooled off but not resolved. My insomnia isn't as severe: I do still get the adrenaline (or whatever) surges waking me up in the middle of the night, but they aren't as primal as they were. A few weeks ago I would wake up at 4 AM feeling like masked men had dragged me out of bed by the hair: my heart would race and my legs felt a couple of live wires that'd been cut out of the wall and were spitting electricity all over the place. Those wakeups were so rough that none of my meds could get me back to sleep, let alone merely lying in bed. I'm still getting roused at 4 AM by that adrenal surge, but my heart rate isn't up and at least half the time I can fall back asleep with a smile, a little self-reassurance, and some deep breathing (and sometimes a Seriphos). I even managed to fall back asleep at 8 AM a couple of times, which hasn't happened (without prescription drugs) in over a year!

* I didn't realize how often my adrenaline (or whatever) was surging, but I was probably having flare ups a dozen times a day. Now it's more like two or three. When I was in the teeth of this thing earlier this year, I obviously noticed the attacks in the middle of the night because they were so badly ravaging my sleep, but I was shrugging off the ones that hit me when I did exhausting things like eat, walk to the corner store, or pick up an Amazon box that had fallen off the porch into the bushes. All this week when I've done everyday tasks I've noticed that I feel fine, and it hit me that I hadn't felt fine at all before and the reason I hadn't felt fine because my nervous system was lit up like a circuit breaker. I hadn't even noticed half the hormonal havoc I was subjecting my body to! I'd normalized it all.

* My legs are very, very sore, but in a different way, like they're finally getting a chance to repair at the roots. Of course I'd been sore during all the training, but I was able to push through it with caffeine, sports massages, yoga, ice compresses, and sleep meds. This soreness feels different and must've been something my body had to override to meet the demands I made on it; on some level I wonder if my adrenal system is so haywire because I was forcing my body to run on it, instead of normal, healthy energy like food and muscle glycogen. Maybe adrenaline was the only thing that allowed me to press through the deeper structural damage I was inflicting on myself. (Earlier this year I tried a Thai walk-on-your-back massage to see if it would help with my hamstrings, and the therapist was worried and told me I had the tightest leg muscles she'd seen in ages and that she was afraid to bend me in some typical stretches because she thought they might snap. I laughed at that at the time, but she must've been right.)

* A lot of the OTC treatments I thought were exacerbating my symptoms were actually lessening them! I tried stopping kava, tulsi, and Seriphos in various combinations this week, and every time I did my symptoms got worse. Kava works especially well: I tried a heavy strain on Friday and a light strain on Saturday and somehow had NO adrenaline surges either day, even at night! (Unfortunately kava does not prevent the short sleep 8 AM wakeups, but it keeps me asleep from 2 AM to 8 AM and chills out my adrenals the rest of the time.) I talked to a kava guy and he told me I had the scary tight chest after kava because I was taking it with amitriptyline fresh in my system (whoops, turns out amitriptyline has a 20 hour half life), apparently a common kava interaction. I cut that out and no more tight chest, hell yeah! As much as I love the kava and can attest to its power, I'm still trying not to take it more than once or twice a week because of the alcohol-esque toll it takes on the liver. After I stopped it, the surges returned Sunday and Monday (today), but aren't as bad, so here's hoping. Seriphos also works: it doesn't seem like to stop a surge that's coming - if I take it at bedtime, it doesn't prevent the 4 AM attack - but it does calm me down quickly if I take it immediately afterwards. I've also been taking one in the morning, as directed, to try to help balance out my system, but it's hard to know how much recovery, if any, is down to that.

* Diet and nutrition has helped a lot. @teresa, I think my commitment to nutrition backfired and actually masked my symptoms for a while. Healthy eating is a foundation of my life, absolutely bedrock - when I started doing it a few years back, I was a new man, and I've been devoted to it ever since - and I'm kinda convinced that eating as nutritious a diet as I do kept me able to train as foolishly as I was when my body should've just collapsed. I eat my take on the Joel Fuhrman food pyramid: 30% fresh veggies, 15% low-fructose fruits, 20% beans, 20% nuts/avocados/seeds/cacao/yogurt, 15% grains. I try to get all my nutrients (except B12, D, and DHA/EPA omegas, which I have to supplement) from food. I don't have any vitamin, mineral, or iron deficiencies, I have test results to vouch for that, and the most surprising thing is that not only do I not have low bone density (one of most common symptoms of overtraining in men and women), I actually still have really, really HIGH bone density, like in the 99th percentile of the population per my last Dexa. I have to imagine that's down to diet. That said, while I was eating healthy food, I was not eating nearly enough. Reading up on the Female Athletic Triad, I learned that to nourish themselves adequately for the stress of training, female athletes are supposed to eat 45 calories per kg of lean body mass IN ADDITION TO however many calories they burn working out. No standards have been established for men, but for me that would've been 45*72 + 2250ish on training days, or ~5500 calories. I was eating 3000! NO FUGGING WONDER my metabolism went to hell, I lost all muscle above my waist, and I was hungry enough to gaze at fast food billboards and dream of climbing up to gnaw the photos. Now I'm eating 3300 a day on zero exercise and I've actually lost fat this week for the first time in 2020. Go figure.

Anyway, sorry to any innocent passersby for the info dump, but I hope it helps anybody else who's dealing with this. I'll update the thread when I get my test results. With any luck I'll be able to report precisely which part of my poor abused endocrine system is revolting, and what treatment the doc advises.