Earthquake or Out of Body Experience vibrations?

Whenever I practice more earnestly relaxation to try to have an OBE, I will regularly experience some form of violent shaking, very short in duration, usually when I just fell asleep in a relaxed state and suddenly snap back into my body.

No later than yesterday, I was relaxing lying on my back while listening to a Monroe Institute CD. During the process, I fell asleep but was soon woken up by a violent shaking of my right leg (1~2 seconds only). I knew the feeling, so I was happy to welcome this small "peak experience" during my practice.

This morning, I was listening again to the Wave 1 / Discovery CD. I listened to one track while lying on my back, but I was a bit tired and couldn't properly sleep on that position. So, I listened to the second track lying on my side. Sure enough, I was soon asleep... only to be woken up by a shaking of my whole body. The shaking did feel like an earthquake, but given the context, I was not fully sure. It did feel different from my usual OBE practice vibration

I checked the time and got up: I knew the Taiwan Central Weather Bureau would soon have data if it had been an earthquake. Sure enough, I found the record of a 6.5 earthquake which in my city registered as 2 on the scale:

Oh, well. Nobody was hurt, and maybe next time I'll experience bona fide OBE vibrations...