> At what point does difficulty motivating yourself to do something unpleasant become an actual pathology?

At the point where it causes a significant and ongoing problem in your personal or professional life.

"Lost track of time and wasted half an hour on HN" - Not a pathology.

"Wasted half a week on HN and was unable to stop even though you really, truly wanted to get your work done?" - Maybe pathology.

"Did that most weeks for months on end." - See a doctor.