Does anyone else ever shake uncontrollably when they wake up too early?

This rarely ever happens, but it seems like whenever I have to wake up extra early, I shiver really hard (I don’t know how else to describe it), but it’s not because I’m cold. This really only happens when I need to be up at some crazy hour like 4am for a road trip or something, and it goes away after 30–60 minutes. I just can’t stop shaking for at least that first 1/2 hour. Has anyone else experienced this? What causes it?