Has anyone done a meditation enema?
Yes. In fact thet're my most satisfying, rejuvenating and energizing enema sessions whenever I don't happen to be sexually stimulated.
Just as rtenesup wrote, I really can't say whether such a mindset may be classed as zen because the word describes a lifestyle as a whole rather than an isolated state of mind more closely related to samādhi. Nevertheless I always sought after utter relaxation and ever since my early administrations I often let myself slip away in a meditational state during the enema - long and slow fillings have always been the best way I conceive to enjoy to the fullest a most special treat which adds to the well-known fresh feeling from internal cleanliness a deeper level of inner clarity so to speak. Now the average skeptic may think of it as a different form of placebo, but achieving a consistent state of α waves following the first few minutes of modulated brathing and the exercise of voiding one's mind from recurrent thoughts and worries about ordinary everyday activities goes a bit further actually and perhaps is indeed some form of sense training which helps to approach the higher levels of awareness closely associated, even if distantly, with the notion of zen.
Even if I learned early on, perhaps unconsciously following my trait, to immerse myself into such a pattern, it wasn't until about twenty years from my first forays that I chanced to converse and exchange thoughts with a young female yoga teacher which at that time was offering free demo lessons to small groups of subscribers at a local community center as a promotion for her courses. She taught us some asana (positions), the basics of defocusing the attention in order to obtain a mental void and showed to the class the typical breathing technique to be exercised both at the beginning and at the end of a yoga session.
After the class left the room I entertained myself a little longer to ask her some specific questions upon comparing my personal relaxation pattern, based on an ongoing switching between the three respiration centers gradually leading to shallower inhalations, with the one she taught which is based on a four-phase alternate nostril breathing with timed pauses. When finally I told her about my five-minute pattern which together with total body relaxation allows me a quick transition to slowed down heart rate while I try to “turn down the volume" of my brain activity by imagining myself lying down on a beach lulled by the seawaves (to justify the rhythmic small body shift due to breathing), except for the substantial difference between the traditional therapeutic basti of ayurveda tradition and the ordinary enemas I enjoy, she plainly explained that what I had been doing since long is a personal interpretation of a recognized technique called visualization, which in turn can be related to yoga exercises as well as to a zen mindset.
Among other noncommittal circumstances this is the drill I follow whenever preparing for a gig after going over my parts and the usual warmup - the latter even more mandatory as years go by… 😁