This isn't really what people are talking about. I see fatigued divers... young, healthy, people turned near-comatosed and catching zzzzz's during surface intervals and on return in the boat from dive trip... and that's in benign, tropical waters on leisurely dives. They do, of course, have unrefined dive profiles and sloppy ascents....
The same was true for me, before I learned how to refine my dive profiles and ascent strategies.... and I was conditioned to some pretty extreme (cold, high exertion, endurance) non-diving activities.
Nowadays, I only experience that type of fatigue or malaise when I'm running shallow skills sessions - that inevitably look quite saw-toothed in profile and often include numerous full or partial ascents. In contrast, I feel vital and fresh in the aftermath of demanding technical wreck penetration decompression dives - despite them being significantly colder and more mentally / physically demanding.
How does a longer, colder, more physically demanding dive leave me feeling fresh and alive; wheras shorter, relaxed, shallow and warm dives leave me drooling?
The answer isn't in the calories burned..... the culprit arises from the effect on our complex physiological immune-system and brain chemistry mechanisms from decompression stress; which results from the excessive microbubble creation brought about by bad dive profiling and unrefined ascent behavior.
People will keep simplistically blaming post-dive fatigue / malaise / reduced vitality on the normal scapegoats; cold, exertion and burned calories. It's just a set of blinkers in the denial process that stops us acknowledging that we are not off-gassing sufficiently to avoid noticeable (if non-injuring) physical and physiological repercussions.