I know the feeling, Allstories. o_O Last year when I started taking Japanese, I'd start saying "Ohayo" in French class and "Bonjour" in Japanese. xD; The fact that my teachers' names (Niiro-sensei and Ms Nero) were pronounced the exact same really didn't help.
But... after a while it gets a lot easier. o_O I guess I kinda work in the sense that I like... switch my brain over so even my thought process is in the other language. xD So it gets easier to switch languages the more I practise. I hope I won't mix languages up too much when I learn more, though. o.o