Hey. I feel identified with your history. I hyphotesis too, that my stutter has it roots on my home life. My mother and my brother have strong personalities to say the least. Exercise help me as well. I think I get more relaxed and confident. Being tired definitely boost stuttering. I have heard that one before. Is very common. Great observation made by your friend. Don´t know the why but you can help yourself ensuring a good night sleep. Here´s an advice: Because I know when I´m tired I stutter way more, If I sense I´m too tired I try to do the least posible then sleep/relax. Anything not vital or priority I postpone it. To rest is fundamental. With that behaviour, I´m trying to be more restfulness on a day to day basis. I do not think is a jaw issue. You said it yourself. Sometimes you speak perfectly normal. Probably when you are alone too. It is more mental combined with some neurological than anything. What has work for me is trying to treat the root. The trauma. Writting is a great tool that I have encounter recently. It is doing wonders. Try to bring to the light your mental problems. Write them down. Don´t care about the spelling or grammar or anything. Just write and write until your wrist wear off. Don´t think about your writting. Don´t try to think the next word or sentence. Just writte and see what happens. Well, I leave you with Dr. Huberman insights on writting and journaling as it is call; It is great and cheap. Worth the try. https://www.youtube.com/watch?v=wAZn9dF3XTo Hope you get better. Take care.