ASD thing. It's called "stimming."
Done it all my life. Sway side-to-side in a lemniscate (∞) like Stevie Wonder and Ray Charles, or rock back and forth on the balls of my feet. Sometimes, standing in a cue, I will bounce up and down on my toes. If I'm just sitting and waiting, I rock back and forth or my legs bounce like mad.
It probably looks odd, but I can't really stop for more than a few seconds at a time - it makes me very agitated and jumpy to not do it. I just have a naturally elevated anxiety level and it helps sooth my nerves. Several times over the years, before I was diagnosed, or even knew what AS was, people at work would stop me in the middle of a conversation to say "Can't you stop that, you're making me seasick - what are you, autistic?"
However, I don't do it if I'm focused on a task. When I'm reading, or drawing or tattooing or using the computer I have no problem being still.