FYI, my son had an overnight stutter appear, which got worse for about 2 weeks to the stage he was giving up speaking because he was so frustrated. A few days later it started decreasing to basically non-existent, he was 2or 3 at the time, now he's 5 and occasionally, like once a week, he'll say something like a stutter or double/tripple word repeat. I've got a very mild stutter (a few family members do) and can mask it 99% of the time unless I'm really excited etc. Anyway, it was fucking scary at the time. We booked in to a ST and she did some tests and got stuff organised, but then we didn't end up needing it. Any family have a stutter? Billingual family?(we are french/eng and thought maybe it overwhelmed him) TLDR: try and not stress, it might disappear, brains are weird. Book in with speech therapist asap. Stutterers are generally smart people :)