Hey there. I spent a couple of years at a FAANG as an engineering manager. Impostor syndrome is extremely, EXTREMELY common. I had it, my peers had it, my direct reports had it. It's normal. Senior-level folks from non-big-tech companies tended to get hit especially hard, as their prior experiences and successes did not necessarily translate to FAANG processes and expectations. It's definitely a bit of a sink-or-swim situation, especially if you came in at a senior level, but take a few breaths, realize that everyone goes through this, it does get better, and be kind to yourself. Good luck!