I’m no doctor but I’d suspect the slack muscles caused by that anaesthesic would quite quickly have worn off. Maybe misalignment ‘just happens’ in some people as they get a bit older. Maybe surgery can cause . I think I’ve heard that with sinus surgery procedures. Btw that type of misalignment is referred as ‘Vertical Heterophoria’ and it’s certainly a firm favourite for treatment by opticians with prisms in some countries. I understand from conversations with my ‘tame’ optician VH is the rarest type of misalignment but of course that doesn’t mean it never occurs.
Most misalignments are congenital so the brain adapts to them and most people never experience further problems of any kind balance or otherwise providing the person had some 3D vision early on, or so I was assured by one top eye specialist I saw. Knowing what we all know of VM and just using common sense it’s therefore logical to assume any misalignment that occurs suddenly, caused ‘by accident’ say, could possibly cause problems. Though with all that we now known about neuroplasticity one could assume, as the new state would be a permanent and therefore stable one, the brain would most probably soon recalibrate unless of course something unstable, like VM, was present to interfere with the process.