I think the most likely explanation is the high altitude illness know as Cerebral Edema, swelling of the brain. The classic field test for this (not always possible when climbing) is to stand with your arms reaching out to both sides, then close your eyes, and touch your nose. The reason this is a good test is that the motor cortex of the brain is the first thing that is affected by the swelling of the brain. It starts to not work well when it is squeezed. The vision center is also sensitive, but usually balance is the first to go. As you describe that you felt ‘drunk’. This is the classic description. I suggest for any peak above 5,000m you add some extra time for your acclimatization. Everyone acclimatizes at a slightly different rate. You are learning what you yourself can do. Elbrus is very easy to ascend too quickly. Many people have these problems there. It is also making sense that the symptoms disappear at 4,000m. You descended and so the brain swelling (Cerebral Edema) was reversed.
Good luck and climb a bit more slowly to high altitude next time and I think you will be fine.