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.
Nitwit! Blubber! Oddment! Tweak!