What language do bilingual people think in?

I'm an idiot I know. But seriously, what languages do you guys think in? Do you think in your native language or the last one you learned? Do you have days when you think in one but not the other? Do you think in both and not differentiate? Let's say I have Russian as my native language (I don't, purely hypothetical), but I'm in America and know English. Would I think about the world around me in English or Russian? Or is it one of those things you don't really consciously think about so you don't know? It's like 2 AM for me here I'm so curious now.