I do agree that many games end up being more tiring than relaxing, but there are also many that don't. In my experience, games involving monotonous grinding make a game more tiring, while strong story elements or just the right level of challenge (not too easy, not too frustrating) are relaxing.

I view a good story-based game essentially as a form of storytelling, no different from reading a good book or watching a good movie. (I take it you don't require a cite for the claim that those are relaxing?) With the capacity to blend movie-like visuals and unmatched immersion, games have the potential to be the ultimate form of storytelling, better than any movie or book.