I think it’s usually one of three things:
- Nervous energy
– Habit
– Restless leg syndrome
I think there might be a genetic element in some cases.
One person I know who can’t sit still easily is also somewhat OCD. She taps her foot or moves her leg or taps her fingers, just always doing something.
I can tell you when I am overmedicated for my thyroid I don’t sit still easily, although I don’t tap my foot or jiggle my legs. My normal is to be calm and can sit for hours. When you have control over how fast or slow your metabolism is, and basically can ramp up or ramp down your hormones that control your entire body system like thyroid patients can, it becomes more obvious the effects. Some people don’t have a diagnosed problem, but they are cursed with being in the normal range, but close enough to the edge that they have symptoms.