I'd say it's definitely not that you forget how to move your tongue! You do seem to describe two aspects of a block well enough, though. The first is that we can sometimes anticipate that a stutter will likely appear, whether by habit or by some sensations leading up to the stutter (this is tricky notion, and we don't have much science on it, I think). The second is getting caught by a stutter, or being surprised by it, and finding yourself in the middle of something that you just can't get through or get out of. Perhaps a third aspect is stumbling through a stutter and landing on the other side of it, without much time to think about what went wrong or what you might've done to get through it. All of it can be terribly confusing, of course. Some people likely also have very different emotions from it - maybe some shut down entirely, and don't even move through the stutter in any way like the above, or others might get angry and start showing it. It's a peculiar phenomenon indeed - hard to get acquainted with.