I imagine that many psychologists looking at this would try to intellectualize this on a phenomenon level - that is to say they want an intuitive explanation like "the self is shutting down and blocking joyful input because it has received too much stimulation" (really random horrible example), but there's probably no way to really understand this intuitively like there is with a person being acutely depressed after a loss of a loved one for example. They miss their loved one, fairly easy to understand although there might be complicating factors like guilt or regret if they didn't leave on a good note or get to talk about something that they meant to, but at least that's intuitively understandable. With LTCs, there's probably something specific (or multiple things) going on at a biological level that have no real purpose, no rhyme or reason to it.
But whatever the abnormal biology is, it can then go on to cause phenomena that it might help to try to think about intuitively. For example, LTC causes a lot bad symptoms, then people worry and ruminate. Some of the same biology that causes the symptoms probably causes biology that's more conducive to rumination and over-thinking as well. We can at least intuitively know that the over-thinking, if present in an LTC sufferer, is bad (and you might have been doing it before as well, just not over-thinking about negative things that stress you) and we can know that the over-thinking is contributing to the LTC or perpetuating it, and therefore we should try to do whatever we can to curb all the over-thinking.
