Loved the beautiful and moving poem!
I am so sorry for your loss, OP. Kudos for you for giving your guy a quick ticket out and avoiding longer suffering.
However rough it appeared, I wouldn’t assume that anything necessarily “went wrong” or that the horse suffered, unless the vet says something did go not as planned.
I am all for euth when the situation is right, but I do think anyone in attendance needs to be aware ahead of time that the horse may struggle. It seems people don’t always know what to expect, and in fact may be expecting something else. It doesn’t mean the horse is aware of what is going on. As someone said, it’s a biological reaction, not a conscious reaction.
For that reason I don’t think the owner needs to feel it is important for them to be present at a euth if they are reluctant to witness it. (Exception would be an inhumane vet like the brutal one described above, just to protect their horse.) I don’t believe it makes any difference to the horse - the whole point is that they don’t know what’s happening. The owner can say their good-byes at a calm and peaceful time.
Although it is hard to see a horse reacting in a rough way, compared with a slow death by inches of old age or some infirmity, euth is still quicker and more humane.
The vet that handled the first euth I attended explained everything wonderfully in a phone call ahead of time. He explained that it is a myth that “animals pass away painlessly in their sleep”.
The vet explained that natural death is frequently agonal and protracted. Organs don’t all give up quietly at the same time. Death is often a slow and painful process as things fail one by one, and the animal is aware of it and may be fighting it. It can go on for many hours or even days.
However rough it may seem at the time, euth was more merciful than the alternative in all of the cases I personally know.