This is what I was always told when I was younger. That my brain processes too fast and my mouth can't catch up. It was really frustrating when people told me to slow down and think about what to say because I already had the reply lined up!! As I get older though, I don't know if I agree if that's the case for me. But maybe it is because it definitely gets worse when I'm stressed in my day to day (instead of one stressful moment) so I'm thinking about a lot of things all the time.