Resting always makes my sleep better (eventually, it may take days).
Exertion always makes my sleep worse.
This.
When well rested I have a sort of bi-phasic sleep, i.e. go to sleep ok, wake around 3am for a while, go back to sleep, wake around 5.30 am. Don't feel refreshed exactly but definitely somewhat better than the evening before.
With PEM it's a very different story: I struggle to get to sleep, then sleep 90 minutes, wake 90 minutes, and repeat until 4 am or so when no more sleep is possible. Or, if it gets really bad one session of 90 minutes is all I get, if that. Definitely not refreshing.
Back in the days before I got the pacing thing sussed I had sleep problems all the time, i.e. I was never rested well enough to sleep. Completely incomprehensible to any healthy person.
Sleep problems have also changed over time. I had some years with hypersomnia. Later some months of day-night reversal that fortunately re-reversed itself, and now insomnia. No idea what caused the changes.
I practice very good sleep hygiene (minus the exercise advice typically included) because it helps on my better days when it's hard to resist the temptation to use my brain when it's actually working for once. But with that comes the risk of it going into overdrive and that can then stop me from falling asleep. So sleep hygiene is really good for that. But it's completely and utterly useless as soon as PEM enters the picture.
I don't use sleep medication though I did try some in the past. The effect was just as paradoxical as my sleep patterns. Zopiclone would first keep me hyper-awake for 4 hours then send me into a coma-like sleep for 2-3 hours from which I'd wake feeling worse than before and that was that for the night. The sedating types of antihistamines and melatonin may have been mildly helpful for dropping off to sleep initially but not for staying asleep.