Yes, another of these threads, unfortunately. I am grappling with this decision and would love some outside perspective.
25 Year old Appaloosa gelding, who I have had for 20 years. Retired at 9 (advanced hock arthritis) and has been living the good life since then, hanging out, giving occasional pony rides to children and old folks, the usual.
In 2018 he started to have Sidewinder type episodes - we did all the testing you can think of short of spinal taps - I work for a vet so no expense spared. EPM negative, no real neuro deficits - though when he has had the episodes he does go on anti-EPM meds and high dose Vitamin E. The episodes would last a few weeks and happened maybe 1-2 times per year. He was his usual self otherwise - sassy, loving eating, appreciating grooming, etc etc, just walking sideways and reluctant to weight bear on one of his hind legs leading to a very pronounced lean (things swapped back and forth as far as which way he was leaning) that he’d ease by leaning on walls when things were at their worst. The episodes would subside within a couple of weeks and he’d have months of normal life with no deficits.
Fast forward to this year, when he started up with an episode in mid-January. We did the usual EPM meds and vitamin E just in case, and added acupuncture to the regimen to give him some relief. Initially the symptoms went away in their usual time frame, but they have come back and been relatively constant now since then. To this point neuro exams have been unremarkable - he knows where his feet are, and he is still lying down nightly and getting up again ok in the mornings. He’s been ok for the farrier up to this point, but at the last trim (2-3 weeks ago) he violently opposed to having his LH raised and manipulated. Farrier is excellent, competent, and patient. We put him on daily Gabapentin to see if we could ease some of the obvious pain he’s been in, and while it seemed to work a bit at the beginning, it hasn’t been a magic bullet.
In the last week, things have progressed. The lean is incredibly pronounced and he’s not as confident in walking around, making me worry about one of the legs giving out or him falling and breaking something. I think the hardest thing is that his demeanour has deteriorated - he has been depressed and agitated at times, but ok at others. He’s become a bit headshy at times as well, which is not normal for him. Thankfully he’s eating normally.
I have the vet coming out today to assess, but I am worried we are nearing the end. I am not someone who keeps animals alive for my sake - if it’s time, it’s time. I’m just riddled with guilt and anxiety about whether the decision to euthanize is a selfish one, because I can’t stand to see him suffer and my absolute greatest fear is him getting into an emergency down situation, not being able to get up, and suffering until he can get help. As silly as it may sound, I’m also vegan and being responsible for the death of an animal is weighing heavily on me - moreso from a “is it the right time?” perspective than anything else.
I guess I’m looking for a bit of support and perspective here. On the investigative/medical side I’m confident we’ve done all we can - Sidewinder is an elusive symptom of a myriad of diagnoses and we’ve looked into every one save going the biopsy/spinal tap route. We are pretty confident there’s some deterioration/pain going on in the lumbar spine/pelvis that is causing him to load one leg much more than the other. We are lucky to have a vet hospital within a 30 minute drive but I’m not comfortable with the idea of him getting on a trailer in his current unbalanced state and I don’t want to give him added stress right now being in a new place with new people (he’s always been a bit of a delicate flower when it comes to vet work).
Thank you for reading and for your thoughts 
