Do you put up a face to present to a certain audience? If yes, you're an imposter. There is no "syndrome", "disorder" or "chemical imbalance". You feel like an imposter because you know deep down that you are being one.
Maybe you have to hype up your image to compete in the market because everyone else also does the same. That does not mean you are not an imposter. It just means everyone is.
Do you feel like an imposter when you are with your dog or your child or a very close friend or relative? If no, you don't have "imposter syndrome".
Just stop being an imposter and you will stop feeling like one. Not practical for you to do that? That's fine. Maybe you do need to put up a face to survive or thrive. Just embrace it.