Why do I stutter less when I just woke up?

Why do I stutter less when I just woke up? I don't actually stutter when I speak, it's just that sometimes I can't get the words out and I have to wait 3-4 seconds. This may have a different name in the literature, I don't know. The thing is, within 30 minutes to an hour after waking up, I can speak properly with almost no pausing. I wonder why this happens, is anyone else in this situation?