Thanks, and yes it is hard to tell for sure what is causing what (particularly since as you alluded to there is a huge variation between people when it comes to sleep). When I'm sufficiently rested in general (at least relatively speaking) I'll usually see the effect that has been noted in depression that sleeping less one night makes me more alert the next day (at least for a while - sleep deprevation usually makes me crash earlier in the day and makes later days worse) and like many people I often find that sleeping more than usual can make me feel more tired the next day (however, it still has quite a positive effect beyond that day). So even without considering medication deviations from usual can have differing short term vs long term effects.

I often get weeks of < 5 hours of sleep a night most nights where the effects of sleep deprevation are huge and all of the sleep medications I've tried that let me sleep longer all have a positive effect on that functioning (I stay away from the GABA-A receptor agonists due to the various negatives and addiction potential, however I've heard a number of others say the same thing about them; I have tried a bunch of unusual stuff). The effect of the sleep deprevation also feels different from the direct medication effect and at least I would expect that sleep quality issues would feel more like sleep deprevation.

Diphenhydramine is one of the better ones for me, but remember the half life is only the half life (except that it doesn't necessarily decay fully regularly like radiation, there is often a point where it gets fully cleared fairly quickly). I've noticed that even balofen (helps me stay asleep), which has a shorter half life, will loose its effectiveness much faster if I take it every day vs. every other day and two days off is better. Taking it for more days at a time requires more days off to recover effectiveness. Again hard to tell what is causing that (part of it for sure is "resetting" the adaptation) but it does often seem to have some positive residual effect the next night (particularly when taking it multiple days in a row).

On the other side, low dose doxepin has a long half life and completely wipes me out during the day (although so do some second generation antihistamines so it is possible there is some unusal indirect effect). When I stoped taking it after most of a month of daily use I felt much better than usual during the day for a few days (I'm guessing this is what pitolisant (Wakix) feels like) even though I wasn't sleeping much at night (the reason I haven't tried pitolisant :/). During that month I took doxepin it gradually had less effect but I generally got better sleep than usual and the tiredness felt different from the sleep deprevation tiredness.

Diphenhydramine if anything affects me in the morning and more with higher doses (the commonly recommended dose for sleep is way to high IMO, half of a fresh 25mg tablet works well for me, a full tablet even fairly old has the groggy effect the next morning; I do generally seem to have a very slow metabolism, though). I try not to take it too often since it has some widespread effects and may not be all that healthy.

Two weeks of consistent use max is what I've seen recommended as well, although in my experience it is much better to avoid taking anything consecutive days if you can help it. Also, the lowest effective dose is best, often the recommended dose is higher than needed.

Sleep issues can cause cognitive decline (it has for me certainly) so that also is hard to tell what is causing what. It is hard to really acknowledge cognitive decline (to yourself even) and I suspect trying to improve sleep in some way is an instinctive response. Alcohol and marijuana both potentially have some short term positive effects on sleep but may be damaging in various ways long term (particularly alcohol) and more so with heavier use. I think marijuana could potentially have some legit sleep use but it is often very pesticide heavy at this point and it also seems fairly addictive. For alcohol, in addition to being addictive it has quite the negative liver effect and I think the liver and kidneys are underappreciated when it comes to sleep quality (actually doxpein seems to be not that great on the liver either :( ).

That is my thinking anyway, thanks for the discussion.