Yea ditto what muttly said. Just visit your local speech language pathologist (SLP) to be sure. But to answer your question, from what you described, I'm not too sure you have a stutter. You mentioned it's a mental block? It could also be a form a aphasia ie brocas aphasia? And SLP would know. Stutterers have what's called speech blocks. It's more physical in nature rather than mental. We often have a lot of tension in our throat, tongue or lips when we try to say a word because we try to force the word out through physical exertion in our speech musculature. We can also have a "mental block" where we can tell we're going to block on a word before we say it, it more so anticipatory / premonitory.