he can sleep for a while until his brain makes sense of it and then it is back to being 'switched on'. I realise that this is just me creating some narrative to try to make sense of what is going on and, likely, this is not at all what is actually happening.
I think we develop a tolerance pretty quickly for things that help with sleep and that our body's goal is to return to what it seems to think is normal, not sleeping or not sleeping well. I develop a tolerance pretty quickly to almost everything that helps me with sleep so I try to keep different tools in my sleep tool box. I think this is one of the cruelest illnesses - not only does it destroy our days, but our nights too . . .
Anyways, here are some things that have helped me with sleep. Also - it seems to me that in general I don't develop a tolerance to amino acids or vitamins. It's mainly herbs and antihistamines which do cause this.
Niacin (the kind that makes you flush) - I discovered maybe 15 years ago that this helps with sleep onset. It helped my sister too, who does not have ME/CFS. I take it every night and don't develop a tolerance. It can cause a flushing reaction which I tolerate because when the flush subsides, I generally feel more relaxed and its easier to fall asleep. I take 500 mg. before bed and 200 mg. more middle of the night. I don't recommend you start with this dose - we're all different. I'd try 50 or 100 mg to start with and see how he does.
Inositol - I take 1 or 2 grams before bed, more middle of the night. This article talks about safely taking much higher doses:
https://www.healthline.com/nutrition/inositol#dosage
5-htp - I take 100 mg. before bed
l-theanine - I think this helps a little - I take maybe 200 - 400 before bed, more middle of the night
melatonin - 10 mg. before bed
generic for Unisom (doxylamine succinate) - this is an old, but powerful antihistamine. When I first started taking it, 1/4 tab would put me to sleep. And I really don't feel bad the next day. Unfortunately tolerance develops rather quickly but I can usually take it for about 10 days before I have to switch off. I highly recommend it. I hated benadryl, it made me feel crappy the next day and didn't help much with sleep.
wild lettuce - herb which can help for awhile, and then stops
Shui de an - again, temporary help
https://www.modernherbshop.com/For_Insomnia_and_Anxiety_Relief_p/shuideancapsules.htm
Seriphos (phosphorylated serine) - this works well to reduce high cortisol in the middle of the night. I would not take it without an adrenal stress index test, which will show if he has nighttime cortisol, which can cause severe insomnia. At one time I had to take 8 capsules (a very high dose) for middle of the night insomnia. But most people I hear from react quite a bit with only 1 or 2 caps. We're all different. Morning seems to be the best time to take it. And you can do the adrenal stress index test at home - google it.
CBD with THC - California lets you get the "real" THC, but am in Texas now which has variants - Delta 8 and 9. Supposed chemically they're the same, I don't know, I don't care. Again, develop tolerance quickly.
California poppy - can calm down one's system. Herbpharm makes a good tincture but unfortunately I needed a lot and so it got expensive pretty quickly.
Also, if I eat anything MSG-related at night for dinner, it will cause severe insomnia. So for dinner I have to basically avoid all processed foods including mayonnaise and mustard (depending on ingredients). I react to almost everything on this list:
https://www.truthinlabeling.org/names.html
magnesium/calcium ratio imbalances can cause insomnia - I've had it go both ways, too much calcium and too little . . . hair analysis has helped me out here.
Check all his meds (I'm sure you've probably done this already) for "side" effects such as insomnia. I've found I have to read the very fine print on drug package inserts
This thread (all about sleep) might have some helpful tips for you:
https://forums.phoenixrising.me/threads/what-has-helped-you-with-sleep-insomnia-post-links.78501/
Also - I'm hypothyroid, and occasionally I seem to have flipped - become a bit hyper and when that happens, nothing will touch my insomnia until I quiet my thyroid down. I have cut my thyroid med doses over the years, with testing, and actually I need to get re-tested now. I've found
HerbPharm Thyroid Calming tincture can help with calming over-active thyroid:
It's more money of course - I've spent a small fortune on trying to sleep!
I hope this helps some! If I were to try one thing, I'd start with the Unisom (or generic), it might give some immediate relief. Then I'd try a bit of niacin and see what happens, and then inositol -