When I run, my head will shake side to side. It looks like I am shaking my head no with each step. It has gotten better as I have been running longer, but it comes out when I am pushing very hard and especially when I'm very tired. It usually isn't bad enough to affect my vision and I didn't even know about it until people told me. I feel as if I could be more efficient if I got rid of it. I take rather small strides and have a quick cadence, so I don't think it's a product of overstriding.