Language immersion fatigue

I remember from my two years in California that my major nightmare was going into the classroom and starting in the wrong language. It's the same here. Before my lecture, I repeated the opening phrase over and over again, just to get it right. When I am very tired I wonder why everybody around me persists in speaking a foreign language. I notice that I insert Swedish words occasionally, especially conjunctions. I talk Swenglish with Staffan. And when I talk to myself (no, not aloud!) I sometimes stop to think which language I am thinking in. There is just one significant indication that I am not completely native: I always count in Russian.