• It has been especially persistent since secondary school, when I could no longer ace every test without effort and homework loads increased dramatically.

This is interesting but inconclusive by itself.

There's potentially a few different factors at play here. One is that overachievers very often hit the wall where their natural aptitude is eclipsed by academic demands later in their educational career and they haven't built up the study habits necessary to get them through the next phase of education so they tend to go from aceing everything to dragging themselves through on a C average or just dropping out entirely.

Another factor is that as you progress through school it becomes less structured and more self-directed and open ended which can be extremely difficult and stressful for autistic people.

Last of all, as you progress through your academic career, the demands on you increase in other aspects of your life - you take on more responsibilities, relationships get more complex, you will take on employment etc. and this can mean that the monotropic autistic brain just feels like it's perpetually overextended which can lead to a decline in performance and academic outcomes.

• With stuff like school assignments, it's almost certainly pathological demand avoidance (PDA) being at play, sometimes not even deadlines are enough and I turn in things late. BeamBrain brought it up but I knew of the concept beforehand. It however affects me most of the time, when I have to decide for myself on what to do.

There's a whole lot to unpack with PDA and my own hot take on it but in short I think that PDA is too loosely defined and, ironically, it has a tendency to pathologise things like burnout so I'd approach this label with caution and healthy skepticism. Not saying that it doesn't exist or that it's "wrong", just that it can fit a lot of different experiences and it's important to be judicious with how we use the label.

What I'm getting at here, in a metaphorical sense at least, speaking as a person who has been diagnosed with chronic fatigue who is on the path to getting POTS diagnosed is that we need to approach a diagnostic label very cautiously because if it's inappropriately applied it can serve to obscure the nature of what you're dealing with, which is counterproductive.

• I indeed have trouble with delaying things to the last moment. It sucks: I'm either too passive and not doing anything or rushing and wearing myself out.

So this definitely points in the direction of either burnout or undiagnosed ADHD. Or, worse yet, both.

• Yes, yes, yes. Lots of buffering/lagging, also while I am doing something.

This one is super interesting. If you literally feel like there's some sort of physiological or psychological "block" that makes you sort of freeze up or buffer, particularly with transitioning between doing things and especially between physical "boundaries" like crossing through doorways then this is a really big indicator of catatonia, which is very common in autism and it's astoundingly lacking in research and general awareness, even within psychiatry itself.

• I actually don't get around to them often, aside from working out. When I am doing them, what often happens is that I am neglecting schoolwork, it piles up over 2-3 weeks and I then collapse in on myself. Instead i instinctively watch the one Discord server I'm in or play around on Google Maps, it's like stimming behaviour.

This sounds a lot like burnout.

• I hate how I will feel determined to do things when I go to bed and then have trouble getting up the morning after, regardless of how much I've slept. One thing I've noticed is how I often become tired when I get home from school, when I didn't feel the need for rest earlier. Part of me suspects that I simply am not eating enough for all the walking to/from school and working out that I do.

I'd be looking at interception here and I'd try some behavioural interventions like having some snack food like trail mix on hand at school constantly while making a habit out of eating a little bit throughout the day or scheduling in mandatory eating breaks in whatever way structures it well for you - it might mean setting a specific alarm on your phone with a label promoting you to eat or it might mean blocking out eating times in a digital calendar or it might mean literally scheduling in what you're going to eat and when for your daily agenda - find something that "fits" how your brain works and run with it.

I'd also consider scheduling in downtime and alone time to decompress throughout the day. Like library time or spending break time away from others by the pond on campus or putting on your noise cancelling headphones and listening to calming or soothing-stim music. That sort of thing.

Lastly it's worth examining your "sensory diet". I've written comments about this elsewhere and I'll link to a good comment here in the edit once I post this one and dredge up the right one I've made prior (I'm currently on a mobile device so it's not conducive to this stuff.)

Edit: Okay I found what I'm looking for here in this comment but at the risk of seeming self-congratulatory, I found a couple of other good ones that are also worth reading here (it's specific to misophonia but the advice can generally be applied to sensory processing more broadly), and one here (skip to where I start with "that's a big question" and I start discussing habit stacking/habit advice for neurotypical people vs neurodivergent people, although the rest of the comment may have stuff that is tangentially of interest to what I've mentioned here in this comment).

• The order of things is very consistent, but when these things happen is not.

This too points towards burnout but it could also fit within ADHD struggled with task initiation and within catatonia so it's inconclusive.

I also want to add that I often feel like I'm running on auto-pilot and that the sluggishness can be overcome with bursts of confidence and determination, but those happen irregularly. I also have a tendency for perfectionism.

Sounds very much like burnout or ADHD. Hard to tell.

Just fyi this is not intended to be diagnostic of ADHD, not that I'm qualified to diagnose anything anyway, but there's enough in what you've said that would make me want to look at whether undiagnosed ADHD is at play here and to go through an actual diagnostic process to either rule it in or to rule it out.

Oh yeah, and there's a big discussion about whether autistic burnout is in any way different from a form of autistic catatonia (or if parts of autistic burnout actually overlap with autistic catatonia). There's an entire effortpost which is calling my name on this topic.