In which case it really does boil down to how one defines "excessive", since the fact is that in the face of many illnesses, the appropriate and proportionate response is "freak the fuck out until someone takes you seriously." In the face of chronic pain, a reasonable analysis of likelihood can tell you that if you want to function next week, you can't make dinner and do dishes tonight. And it would take a specialist experienced with illness and disability to be able to tell the difference between proportionate and excessive.

The point of the asthma example is that there are people who do disproportionately worry about their symptoms. For the purposes of the example, assume that the person would physically be able to go on these outings without having an asthma attack; they are vastly overestimating the probability out of anxiety and fear. If they are treated with psychotherapy, they are able to make more accurate assessments, and can be more functional. This is a real thing that happens in the real world, and that's somatic symptom disorder. Those people need treatment too. We can't just pretend that problem doesn't exist because it can be overgeneralized.