You might enjoy Mike Cskiszentmihalyi's "Flow: The Psychology of Optimal Experience." I find 'optimal enjoyment' a fascinating topic vis-a-vis his studies.
In general, though, both the philosophy of optimal enjoyment, as well as 'its' neuroscience are lacking.
And while the relaxation response in warm pools can be optimal for me, exploring the relaxation response richly elsewhere also has benefits.
I wonder if we can cultivate kinds of vision, that can take on the vivid qualities of hallucinations or dreams, in specific, ongoing ways, that are also helpful, and seem benign, to people vis-a-vis optimal enjoyment. How might this give rise to a language and conversation? Can this process itself also be a 'flow the psychology of optimal experience' experience?