The former category would include not experiencing, or noticing that you're experiencing, 'tiredness', even when your body is acting tired in a way that others would notice (e.g. yawning, stretching, body language).

I'm not sure if this is what you're talking about, but I've long distinguished two aspects of "tiredness". One is the sensation of fatigue, exhaustion, muddled thinking, &c.--physical indicators of "I need sleep now".

The second is the sensation of actually being sleepy, in the sense of reduced energy, body relaxation, and a general feeling that going to bed sounds like a fine plan.

I almost always notice the former, but unless accompanied by the latter (often not the case), acting on it by going to bed requires a conscious decision. Usually, the sleepiness will appear after I'm lying down, but at times I've been unable to clear my mind of activity and will lie in bed for two or more hours, unable to sleep despite being extremely tired.

If I'm deeply involved in something and not feeling "sleepy" I can easily fail to notice the fatigue (along with hunger and various other non-urgent physical sensations).

The second case involves not being able to stop whatever activity you're engaged in and go to bed, even though you recognize (perhaps briefly, before being drawn back into what you're doing) that you are tired and it would be a good idea.

In my case it's more garden-variety procrastination; going to sleep is just one more thing that I know I should do but don't really want to, because it's boring.

I'm curious to find out if those issues are also experienced by people who aren't autistic - perhaps to a lesser degree, or with different explanations than the ones that I mentioned. Do the issues I described sound like what you're experiencing? Are they close, or similar in some interesting way?

My experience mostly reduces to a disconnect between a non-critical physical need and the desire to fulfill it, generally to an extent proportional to how much mental activity is bouncing around my conscious mind (the default state being "too much").

As a final note, besides the melatonin not making me sleepy, neither ethanol nor caffeine seems to have an appreciable effect on whether I can get to sleep (though both will reduce the quality of any sleep).