My sisters and I have been spending a good amount of time on Skype lately. As a result I've begun to think in Chinese. Trouble is, as I go about business, I don't notice what language I'm thinking with. Example: I stop at the post office, before I get out the car, I grab the mails, my purse and sunglasses from the passenger seat, at the same time rehearsing in my mind the questions I'm going to ask the post office clerks. Only one step away from the counter do I realize what is about to roll off my tongue isn't English. My mind moves into emergency mode, dives into a murky backroom and snatches the right English words, whips them into right order, send them onto the airwave. The clerk understands perfectly and answers my question, by which time my mind is all English and I am conducting a normal conversation with her.
Unless you speak two languages, you don't know the fun. Not to mention the languages you dream in.