What can cause a person to wake up with a stutter one day?

What can cause a person to wake up with a stutter one day? When I was in fifth grade, I woke up with a stutter. Sometimes I simply cannot get a sound out. In the middle of a sentence I'll just stop talking, because the I just cannot get the next word out. Other times, I do t-t-t-t-t-this. My friend was asking me about my stutter and he said he wonders if I had some sort of stroke in my sleep and it caused a stutter, but I don't know what could cause this type of thing.