This is relative to the saying "woke up on the wrong side of the bed". It has mostly to do with how well you slept, how you spend your morning, and typically being in a better and more optimistic mood. But there are those days just like anyone else, where you just wake up pissed. Because your mood and level of anxiousness has so much to do with a stutter (being neurophysiological), it matters a lot how you wake up. You can find lots of research on this! It might not mention stuttering specifically, but you can research how to schedule your sleep and coordinate your nights and mornings to pursue a better waking mood. I have this problem too and it blows, so I'll be doing that research as well. Good luck!