This can be a sign of B12 deficiency - anyone had it? It came up when I was reading A Tufan et all, Chyild Adolescen phsyc 2012.6.25 on an adolescent with mixed psychotic features due to B12 deficiency.
I rushed round to my son and got him to shut his eyes while he stood with his feet together. Sure enough, he began to sway and rock - sensory ataxia.
Not proof, of course, but with everything else, a useful pointer.
Has anyone else had this? In this report, it resolved really quickly with B12.