This is has happened 3x in my life. Once at 30 (for 3 months), 37 (for 6 weeks), and 38 (2 weeks). It was full blow fluency and it was amazing. When I say fluent I don't mean "few blocks and was coping well" I mean my stutter was non-existent. It's amazing but it never lasts. I stopped thinking about it because I would become obsessed with the chase.