I've got a fun suite of weird stuff going on^[1], so here's a list of sometimes-very-N=1 data:

1. Napping: I suck at naps. Despite being very tired, I do not fall asleep easily, and if I do fall asleep, it's probably not going to be for just 5-15 minutes. I also tend to wake up with a lot of sleep inertia, so the net effect of naps on alertness across a day tends to be negative. They also tend to destroy my sleep schedule. 
2. Melatonin: probably the single most noticeable non-stimulant intervention. While I'm by-default very tired all the time, it's still hard to go to sleep. Without mitigation, this usually meant it was nearly impossible to maintain a 24 hour schedule. Melatonin helps a lot with going to sleep and mostly pauses the forward march (unless I mess up).^[2]
3. Light therapy: subtle, but seems to have an effect. It's more obvious when comparing 'effectively being in a cave' with 'being exposed to a large amount of direct sunlight.' I did notice that, when stacked on everything else, the period where I tried light therapy^[3] was the first time I was able to intentionally wake up earlier over the course of several days.
4. Avoiding excessive light near bed: pretty obviously useful. I've used blue-blocking glasses with some effect, though it's definitely better to just not be exposed to too much light in the first place. I reduce monitor brightness to the minimum if I'm on the computer within 3-5 hours of sleep.
5. Consistent sleep schedule: high impact, if I can manage it. Having my circadian rhythm fall out of entrainment was a significant contributor^[4] to my historical sleeping 10-12 hours a day.^[5]
6. Going to bed earlier: conditioning on waking up with no alarm, sleep duration was not correlated with daytime alertness for me according to my sleep logs. Going to bed early enough such that most of my sleep was at night was correlated.^[6]
7. CPAP: Fiddled with one off-prescription a while since I had access to one and it was cheaper than testing for sleep apnea otherwise. No effect.^[7]
8. Nose strips: hard to measure impact on sleep quality, but subjectively nice! My nosetubes are on the small side, I guess.
9. Changing detergents/pillows: I seem to react to some detergents, softeners, dust, and stuff along those lines. It's very obvious when I don't double-rinse my pillowcases; my nose swells up to uselessness.
10. Sleeping room temperature: 62-66F is nice. 72F is not nice. 80F+ is torture.^[8]
11. Watercooled beds: I tried products like eight sleep for a while. If you don't have the ability to reduce the air temperature and humidity to ideal levels, it's worth it, but there is a comfort penalty. It doesn't feel like laying on a fresh and pleasantly cool sheet; it's weirdly like laying on somewhat damp sheets that never dry.^[9] Way better than nothing, but way worse than a good sleeping environment.^[10]
12. Breathable bedding: surprisingly noticeable. I bought some wirecutter-reviewed cotton percale sheets and a latex mattress. I do like the latex mattress, but I think the sheets have a bigger effect. Don't have data on whether it meaningfully changed sleep quality, but it is nice.
13. Caffeine: pretty standard. Helps a bit. Not as strong as prescription stimulants at reasonable dosages, can't use it every day without the effect diminishing very noticeably. And without tolerance, consuming it much later than immediately after getting out of bed disrupts my sleep the next night. I tend to drink some coffee in the morning on days where I don't take other stimulants to make the mornings suck less.
14. Protriptyline: sometimes useful, but a very bad time for me. Got pretty much all the side effects, including the "stop taking and talk to your doctor immediately" kind and uncomfortably close to the "go to a hospital" kind.^[11]
15. Modafinil: alas, no significant effect. Maybe slightly clumsier, maybe slightly longer sleep, maybe slightly more tired. Best guess is that it interfered with my sleep a little bit.
16. Ritalin: Works! I use a low dose (12.5 mg/day) of the immediate release generic. Pretty short half-life, but that's actually nice for being able to go to sleep. I often cut pills in half to manually allocate alertness more smoothly. I can also elect to just not take it before a plane flight or on days where being snoozey isn't a big problem.
17. Stimulant juggling/off days: very hard to tell if there's an effect on tolerance with N=1 for non-caffeine stimulants at low therapeutic dosages. I usually do ~5 ritalin days and ~2 caffeine days a week, and I can say that ritalin does still obviously work after several years.^[12]
18. Creatine: I don't notice any sleep/alertness effect, though some people report it. I use it primarily for fitness reasons.^[13]
19. Exercise: hard to measure impact on alertness. Probably some long-term benefit, but if I overdo it on any given day, it's easy to ruin myself. I exercise a bit every day to try to avoid getting obliterated.^[14]
20. Cytomel: this is a weird one that I don't think will be useful to anyone reading this. It turns out that, while my TSH and T4 levels are normal, my untreated T3 levels are very low for still-unclear reasons. I had symptoms of hypothyroidism for decades, but it took until my late 20's to figure out why. Hypothyroidism isn't the same thing as a sleep disorder, but stacking fatigue on a sleep disorder isn't fun.^[15]
21. Meal timing: another weird one. I've always had an unusual tendency towards hypoglycemic symptoms.^[16] In its milder form, this comes with severe fatigue that can seem a bit like sleepiness if you squint. As of a few weeks ago with the help of a continuous glucose monitor, I finally confirmed I've got some very wonky blood sugar behavior despite a normal A1C; one notable bit is a pattern of reactive hypoglycemia. I can't avoid hypoglycemia during exercise by e.g. drinking chocolate milk beforehand. I've actually managed to induce mild hypoglycemia by eating a cinnamon roll pancake (and not exercising). Exercising without food actually works a bit better, though I do still have to be careful about the intensity * duration.

I'm probably forgetting some stuff.

1. ^{^}

   "Idiopathic hypersomnia"-with-a-shrug was the sleep doctor's best guess on the sleep side, plus a weirdo kind of hypothyroidism, plus HEDs, plus something strange going on with blood sugar regulation, plus some other miscellaneous and probably autoimmune related nonsense.

2. ^{^}

   I tend to take 300 mcg about 2-5 hours before my target bedtime to help with entrainment, then another 300-600 mcg closer to bedtime for the sleepiness promoting effect. 

3. ^{^}

   In the form of luminette glasses. I wouldn't say they have a great user experience; it's easy to get a headache and the nose doohicky broke almost immediately. That's part of why I didn't keep using them, but I may try again.

4. ^{^}

   But far from sole!

5. ^{^}

   While still being tired enough during the day to hallucinate on occasion.

6. ^{^}

   Implementing this and maintaining sleep consistency functionally requires other interventions. Without melatonin etc., my schedule free-runs mercilessly.

7. ^{^}

   Given that I was doing this independently, I can't guarantee that Proper Doctor-Supervised CPAP Usage wouldn't do something, but I doubt it. I also monitored myself overnight with a camera. I do a lot of acrobatics, but there was no sign of apneas or otherwise distressed breathing.

8. ^{^}

   When I was younger, I would frequently ask my parents to drop the thermostat down at night because we lived in one of those climates where the air can kill you if you go outside at the wrong time for too long. They were willing to go down to around 73F at night. My room was east-facing, theirs was west-facing. Unbeknownst to me, there was also a gap between the floor and wall that opened directly into the attic. That space was also uninsulated. Great times.

9. ^{^}

   It wasn't leaking!

10. ^{^}

     The cooling is most noticeable at pressure points, so there's a very uneven effect. Parts of your body can feel uncomfortably cold while you're still sweating from the air temperature and humidity.

11. ^{^}

    The "hmm my heart really isn't working right" issues were bad, but it also included some spooky brain-hijacky mental effects. Genuinely not sure I would have survived six months on it even with total awareness that it was entirely caused by the medication and would stop if I stopped taking it. I had spent some years severely depressed when I was younger, but this was the first time I viscerally understood how a person might opt out... despite being perfectly fine 48 hours earlier.

12. ^{^}

    I'd say it dropped a little in efficacy in the first week or two, maybe, but not by much, and then leveled out. Does the juggling contribute to this efficacy? No idea. Caffeine and ritalin both have dopaminergic effects, so there's probably a little mutual tolerance on that mechanism, but they do have some differences.

13. ^{^}

    Effect is still subtle, but creatine is one of the only supplements that has strong evidence that it does anything.

14. ^{^}

    Beyond the usual health/aesthetic reasons for exercising, I also have to compensate for joint loosey-gooseyness related to doctor-suspected HEDs. Even now, I can easily pull my shoulders out of socket, and last week discovered that (with the help of some post-covid-related joint inflammation), my knees still do the thing where they slip out of alignment mid-step and when I put weight back on them, various bits of soft tissues get crushed. Much better than it used to be; when I was ~18, there were many days where walking was uncomfortable or actively painful due to a combination of ankle, knee, hip, and back pain.

15. ^{^}

    Interesting note: my first ~8 years of exercise before starting cytomel, including deliberate training for the deadlift, saw me plateau at a 1 rep max on deadlift of... around 155 pounds. (I'm a bit-under-6'4" male. This is very low, like "are you sure you're even exercising" low. I was, in fact, exercising, and sometimes at an excessive level of intensity. I blacked out mid-rep once; do not recommend.)

    Upon starting cytomel, my strength increased by around 30% within 3 months. Each subsequent dosage increase was followed by similar strength increases. Cytomel is not an anabolic steroid and does not have anabolic effects in healthy individuals.

    I'm still no professional powerlifter, but I'm now at least above average within the actively-lifting population of my size. The fact that I "wasted" so many years of exercise was... annoying.

16. ^{^}

    Going too long without food or doing a little too much exercise is a good way for me to enter a mild grinding hypoglycemic state. More severely, when I went a little too far with intense exercise, I ended up on the floor unable to move while barely holding onto consciousness.