In my experience, the illness in, combination with lack of support and misunderstanding, can easily lead to a lack of pleasant experiences. This deprivation appears similar to depression. I think it would be more accurate to describe it as getting used to having too few good things in life. One gets used to the fact that seeking a positive experience generally does not lead to a positive experience, so there is little drive to do most of the things that a normal person would do to feel good. The few remaining things that give pleasure may be relied upon excessively.
In less general terms, if going outside tends to make the person feel unwell soon, or if the later consequence is malaise, the person will have little drive to do so, except in ways that are within the tolerated limits. But one must first develop an understanding of the dynamics at play... that the malaise is a delayed consequence and not random, that one must reduce expectations and do less than one would like. And one must also learn to resist the requests or invitations of other people to do as much as a normal person would in the give circumstance. Other people and systems tend to have a negative impact when they don't take accomodate the illness. There's a lot of learning involved if one starts from a position of total ignorance of the illness and confusion about what is happening and what to do.
The state of PEM can also look similar to depression.
