Well, for what it's worth, that was my hypothesis as well for explaining my anecdotal experience with this! I switched to effectively speaking English full-time

Well, for what it's worth, that was my hypothesis as well for explaining my anecdotal experience with this! I switched to effectively speaking English full-time in my late twenties, due to having a foreign partner and later moving abroad with her. I've noticed that I emotionally regress a little bit to teen/tween behavior and anxieties whenever I speak Dutch again for longer periods of time. This effect is at its strongest when I'm visiting my parents in the Netherlands, so there's an obvious location-component to it as well. Linking places to emotional states is pretty well established IIUC, so the latter shouldn't be surprise.