I just want to throw one other possibility out there. Everybody has given you great advice and one or more of them might be right.
But I went to a talk many years ago by Kelly Dorfman where she said toe walking could be a sign of an essential fatty acid deficiency.
What luck, I found someone's notes to that talk online:
Here is the part I was talking about:
She talked about essential fatty acid deficiency, some symptoms of which are: wax buildup in ears, restlessness, "permanent gooseflesh", "Albert Einstein
hair", toe walking, and excessive thirst. She recommends Total EFA by Health From the Sun, flaxseed oil, and Efalex Focus as replacements for the missing fatty acids. She says they rancidify quickly, so we should taste them every
other week to be sure they are still good.