An AIDA2 course is two to three days: pool sessions on breath-hold and equalisation technique, theory on the physiology of diving, then open water dives building depth gradually under supervision. It's more technical, and far more physically demanding, than it looks from the surface.
Why it stuck as a habit
The breathing work carries over into everything else — running, lifting, even sleep. It's the one 'holiday activity' from this whole list that turned into an actual ongoing practice rather than a one-off certification card in a drawer.
