To my way of thinking, the last sentence " The upsetting event could even be something as simple as sitting here right now, reading this book, feeling depressed, anxious, or discouraged." can be understood as a description of one upsetting event in which a person is experiencing three things(sitting, reading, and feeling at the same time), or understood as three separate events(e.g. Bob sitting here as event one, John reading a book as event two, Tailor feeling depressed as event three). I am not a native English speaker. I am confused about which understanding is correct. Could anybody tell me which understanding is correct and why?
The sentence is referring to one activity, with the body in a position, and with a feeling that the person is having while doing it.
The activity is reading. The position is "sitting" or "seated". (In England they would even say "you could be sat here".) The feeling is one of these: depression, anxiety, or discouragement.
It may be tricky because of the list of feelings at the end of the sentence, but to me it is pretty clear that the sentence is meant to be understood as: (Sitting here) and (reading) and (feeling [x or y or z])
Hope this helps! Elie