There are some people who interpret most of their experience in pathological terms. That is, they look at each experience they have for its negative and sinister sides, as a sign that they are ill. They sometimes then go on to conclude that their illness is a particular disease entity based on sensitive rather than specific signs. The issue of sensitivity versus specificity is vital here, so I will go into it in some more detail.
When a sign is sensitive, it means that most people with particular illness will have that sign, so it's unlikely that you will miss someone who has got it if you look for it. At first glance that sounds like a good thing, and of course it can be. However, there is also a downside because there are also likely to be lots of people who don't have that problem with it. A notorious example of this is the underactive thyroid, which has all sorts of easily recognised signs and symptoms such as low appetite, weight gain and fatigue, most of which are also associated with many other conditions, meaning that it can be easily missed. In terms of thought processes, sensitivity is akin to paranoia, and here I want to look at paranoia not in pathological terms so much as a state of mind we can all enter which can merely follow from an unusual set of experiences or a habit of jumping to conclusions. In any case, the idea of paranoia as a label for a psychiatric condition is now deprecated in favour of the rather unsatisfactory term "delusional disorder" (don't get me started!).
Then there are specific signs. These are the opposite of sensitive signs. A person with a specific sign of a condition is unlikely not to have it, but there may be many people without that sign who do have that condition. An example, and I've cheated a bit here by making it broader than necessary, is that if someone experiences pain in their lymph nodes soon after drinking alcohol but not at other times, they will almost certainly have a lymphoma. This is helpful for diagnosing them as an individual of course. Unfortunately it is still problematic for other people. Whereas few people with that symptom won't have lymphoma, lots of people without it will have lymphoma, so there's a risk of it not being diagnosed if you focus too much on that symptom rather than others. An example of a mental health issue similar to this is minimising the positive in depressive thinking, although of course depressive thinking also involves sensitive-style thought processes. Reliance on specific signs is also akin to scepticism in the philosophical sense in that you don't start to believe in something until you've eliminated other things it might be. It is in fact an approach I've taken myself in recent years.
There is a tendency for some people, when they take what they hope is a medical stance towards their experience , to plump for sensitive signs rather than specific ones, particularly after a long period of frustration waiting for a diagnosis, because they really want an answer badly. They are frustrated and want not only an answer but also an explanation for their mystery illness. Their motivation becomes emotive in a particular way, where they experience a depressive train of thought leading to a negative conclusion.