Or what would that be called? Pretty much the same things that would usually be considered ableism, but when there’s not a recognised disability involved but just health issue/s (which could be “disabling”).
For example, not believing someone about their health issue, dismissing it or refusing to believe that it impacts their ability to function or can be a valid excuse for things (often solely on the basis that it’s not a recognised disability), blaming someone’s health issue on different things they aren’t caused by (and trying to attribute it to the person’s behaviour as if it’s their fault), and/or claiming that their opinions can’t be taken seriously due to their health problem
Would it be called health-based discrimination or something (despite somewhat mimicking the same mentalities as ableism)?
From the Equal Employment Opportunity Commission, in regards to the ADA:
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.
It doesn’t have to be deliberately malicious to be ableism. It’s often just thoughtlessness.
The social model of disability distinguishes between ‘impairment’, which is some functional limitation, and ‘disability’ which is created by barriers to people with an impairment. Most of those barriers exist because their designers just didn’t think about it and/or were not required to. The building with steps and no ramps, the information provided by written sign only, the flashing lights which can trigger seizures. They’re not (usually) a product of irrational hate, just ignorance and carelessness, and in some cases a conscious refusal to cater for a minority need because of costs or aesthetics.
The effect on disabled people is much the same, whether it was deliberate or careless, of course.
Ableism is so ingrained in our society that folks have trouble even recognizing it. OP is absolutely experiencing ableism, being dismissed and treated differently because of their health issues, recognized and intentional or not, is ableism.
Your example is a very legal perspective of ableism that barely scratches the surface of ableism and makes it difficult to address wider impacts. This is a similar thinking to racism only being legal segregation and the KKK, when it shows up in everyday life in far broader ways.