This is really interesting to me because my dreams are all in French, regardless of who I am speaking with. I totally agree about being stuck in a 'mode,' I refer to it as my French brain, or my English brain (I have guarded in my mind Maori and English as the same language. I can't seem to break this). I am at the point where if someone that I normally speak English with, speaks French to me I find it incredibly difficult to engage my 'french brain' and speak French to them. It's so frustrating!
Yes, very similar. It's as though my mind sees the (normally) English speaker, and says "Right! Access all English words and semantics!" And everytime I go to retrieve French I have to actively think, make exact translations, double check my phrases. It's gets tiring, fast. Then, there will be someone right next to them, that I always speak in French with (and sometimes they are native English speakers, but we haven't spoken English together) and there isn't a split second where I think (actively) about what I say. It just flows out. And its so lovely and enjoyable.