Experiences - Have you ever had 'sewing machine leg'?

[KomodoMK]

Sewing machine leg is when your leg goes up and down, heel leaving the surface but toes remaining in place, bringing your knee up. It is usually quite hard to control and/or stop.

My little fishy used to get this and it seemed to increase in both speed and force with higher dosages and regular use of MDMA. On one night after a big session he was laid back with his friends with 2 feet on the coffee table and it was so hard and fast that it actually seemed/sounded like an earthquake. It was a speed and force that could not be achieved without chemical assistance. For some reason it just feels really good.

It does happen on other stimulants but seems more pronounced on MDMA. My little fishy still gets it now when listening to music he used to listen to when pilling (thus why I made this post) but it is easily controllable when not high.

What are other peoples experiences of this? Anyone even know what causes this?