Baby shaking while nursing to sleep?

My 4.5 mo baby was crying a lot from gas and calmed down. I was nursing to sleep and while nursing both his shoulders down to wrists started shaking - like when an adult is freezing. I placed my hand over his Arm and it stopped but it happened 3 more times. The only thing I can find online is neonatal benign sleep mycolnus but it doesn’t really look like the videos. Has anyone had this happen to them? This is was the first time ever.