I'm no expert but i have seen peoples spiders do this, They call it the wobble i am sure others will pick this thread up really fast. As i have heard its not something to worry about. in some cases you cannot notice it and others like your case its noticeable. If I'm correct the snake is not in any pain, i feel like its if our motor receptors got blocked we'd do the same thing cannot tell whats up and whats down... But again i'm not expert and i am sure some one will pounce on this thread.