Sometimes when they stretch too far, they wobble somewhat, just because it's hard to hold up that much their body for an extended period of time. Based on your description, that's what my hunch is that is going on...but without video or seeing it in person, it's hard to be absolutely 100% sure.

But, my snakes do that too, and almost always when they are stretched out and looking around, they just kinda... wobble. It's not like they have legs to use to brace themselves!

-Jen