when there's not a recognised disability involved but just health issue/s (which could be "disabling").

From the Equal Employment Opportunity Commission, in regards to the ADA:

Under the ADA , you have a disability if you have a physical or mental impairment that substantially limits a major life activity.

Essentially, if you are disabled, you have a disability, whether recognized or not. If you are not disabled, then you do not have a disability.

Under this definition, something like asthma, which is fairly common, can be a disability when it comes to strenuous activities, but isn't something that is immediately obvious to someone just passing on the street.

As far as it being ablist to assume that someone not showing signs of disability isn't disabled? No, that's silly. Not believing them if they tell you they can't run a mile because they have asthma? Still no, that's skepticism.

Ablism would be something like planning a company outing, and choosing the location up a tall, steep hill when other options were available, specifically because you don't like the fact that your coworker has asthma.

Any health issues that affect your ability to do "normal" things is a disability, no matter how severe, but using the term ablist at people is counter productive. It's a great term for describing types of behaviors and attitudes, but it's not productive in a real life ablist encounter. It just makes them defensive and deaf to reason. Work with them to create knowledge and understanding, don't oppose them or accuse them, offer friendly insight into your life. If they accept it, great, if not, move on. You can't control others, don't stress about it.

That said, I'm not sure what you mean by "not recognized". If it's a medical issue of any variety, it's recognized somewhere in the DSM. But it is very popular, especially among young people, to self diagnose and go on as of it's a sure thing. There are crap doctors out there, so one should seek as many opinions as needed, but until a physician diagnoses it, it is ablist to coopt disabilities and misresent what being disabled actually is based on a hunch. The way to act in this situation is to say "I think I might have x, but I haven't gotten a confirmation yet" or something. Totally fine. But saying "I have x" when no physician has told them so is lying to others and themselves for their own ego.

If someone were to make up diseases not recognized by the DSM and claiming it's a disability, this is just as ablist.

I am on permanent disability, unable to work, with severe mental health shit. I live in Canada. If you want more info, feel free to dm me.

Definitely assholery but perhaps not discrimination in a legal sense - but that will be heavily dependent on wherever you are and possibly not answerable outside of court.

Are you asking regarding employment, or just in society at large? In the US, there are laws outlining what constitutes employment discrimination, and I don't think you've given us enough detail to say more.

I'm curious what you mean by "not a recognized disability?" Recognized by whom? Someone with a health condition that impacts their ability to function in one or more life domains is certainly experiencing a disability

Yes.

able·ism /ˈābəˌlizəm/ noun A system of assigning value to people's bodies and minds based on societally constructed ideas of normalcy, productivity, desirability, intelligence, excellence, and fitness. These constructed ideas are deeply rooted in eugenics, anti-Blackness, misogyny, colonialism, imperialism, and capitalism. This systemic oppression that leads to people and society determining people's value based on their culture, age, language, appearance, religion, birth or living place, "health/wellness", and/or their ability to satisfactorily re/produce, "excel" and "behave." You do not have to be disabled to experience ableism.

This is also tied to healthism/health supremacy, recommended researching more about these topics to better understand how they impact everyone's lives, disabled or not.

As I write this, I have some debilitating respiratory infection. It's absolutely a disability at the moment - even if only temporary (I hope lol). I can barely do anything without assistance but most people wouldn't consider it a disability like some others.

Now sickness might be a different case than what you're considering, but I don't consider it ableism for "healthy" people to not want my company right now. I would probably avoid them, too, if the roles were reversed.

if it's not recognized, not sure why it'd be discrimination. sure, anyone can be a victim - but not everyone is.