I'm ADHD... (And like most, but not all ADHD'ers) insomnia is just a part of life.
I 'reset' from time to time with Benedryl. Not addictive, and I can force through it in the event of an emergency. (Shudder, I HAVE tried sleeping pills... Thee serious ones... NOT for me!)
I also have PHENOM sleep on most ADHD meds. (Stimulants... ADHD types have 'opposite stimulant reaction'). But I don't like the other side effects. Sleep, though? I can just decide to go to bed (like needing or wanting to get up early the next day... Get ready for bed totally awake, lay down, and be asleep 15 minutes later. Mind blowing. Crazy town. ALMOST worth the daytime effects. Not quite, though!
I have done a sleep study (couple of them). Fun stuff.
First off if I lay down 'awake' OR 'kinda tired'... My mind leaps into overdrive. Readings off the charts that only get more and more busy the longer I lay there. I have to go to bed EXHAUSTED in order to bypass that. Even still, it takes me about an hour to fall asleep. (if I'm laying down before that I 'wake up' -never really sleeping- in about an hour. My eyes just POP open and I have to start moving. I often describe ADHDc as 'when my body is still, my mind is moving... And when my body is moving my mind is still(.
When I go to bed exhausted? I don't actually sleep, much. I pass out. Unconscious. I don't hit REM / normal sleep until im woken up.
((This works great in infants/toddlerhood and combat, btw... Because if I'm awakened by an emergency, I don't 'fog of sleep'... I got from passed out to fully awake and aware without having to deal with waking up from Rem/delta, etc. like an on/off button))
Typically I only get an 'hour' of REM/Delta/etc per night. From when my alarm first goes off to an hour later of hitting 'snooze' every 10 minutes, just constant cycling REM.
EXCEPT
Once every 5-10 days I'll do HOURS of pure REM. like 9-12.
So my brain is quirky.
Did the sleep study(s) help at all? Not really. I know what's going on... But it's not like I can change my brain. Well, I can. With ADHD meds/stimulants, or allergy meds or whatever.
If it had been Apnea, or something else, though... Easy fix.
Mmmmm... I should add, though;
I dated an LMP for awhile. zOMG. It does the 'movement' my body needs to keep my mind still. So do boats and trains. None of the above do I have in my daily life.