What is it like to know two languages?

To all multilingual ones here, I pose this question: what is it like knowing multiple languages? Do you think in different languages, change when the environment does, or switch between them randomly? Do you ever get your words mixed up (i.e., you're talking to an English speaker but instead of saying cheese you say queso)? Do you find that knowing another language helps or hinders your understanding of your native one?

Pick and choose whatever you want to answer, but thank you for your time either way!

>>23
Yeah, but you don't think in a language. What language are animals supposed to think in? Language is not a medium through which we think, it's a medium through which we communicate with one another. You don't "think" any different at all when you speak to a person in a foreign language.