This can also happen with synthetic cannabinoids, and is not entirely dose dependent. I took a very large dose of JWH-073 over a period of about ten minutes when I first got it because I thought it would kick in very fast like most smoked drugs. I guess that was a stupid mistake, but no harm was done. I did not get the shakes from that, it was just an intense trip and I thought I might be dying or suffering brain damage for a very long 5-10 minutes.
I smoked 14mg a few days later, much less than that first dose. I got the shakes this time. I was in the kitchen when it started. My arms and legs were shaking, and my torso was moving side to side a lot and twisting a little. I barely made it back to my bed without falling. It got more intense after that. It didn't really bother me, though I was worried that this was a sign that the chemical was toxic. I'm glad I found out that weed causes the same thing sometimes.
Later, I got some muscle twitches from an 8mg dose, but it was not even close to the shaking I got before.
Someone else experiencing the same side effect from JWH-018 has posted a trip report on Bluelight.
This side effect may be something that all cannabinoids share in common. It can definitely happen with JWH-073 and JWH-018.