For whatever reason, I decided to transcribe the warmup exercise I made for myself when I was in middle school. Until today, I had assumed it was probably in 4/4 (oops!). Anyway, it was fun to play then and is still fun to play today, and it is kind of neat to see it laid out in front of me after ~30 years.
In hindsight, I have a feeling I must've heard someone practicing "Passacaglia" by Handel/Halvorsen (thanks @krj!), remembered the first phrase, and filled in some blanks when I had the chance, and then took it from there. ¯\_(ツ)_/¯