Yeah, it's pretty tough to deal with day-to-day when you're constantly experiencing those feelings, though I suppose you get used to living with it and don't let it bother you so much overtime (particularly if you've been like that for as long as you can remember; a lot of people with this seem to have it almost ingrained in their personality and self-image, though I'm not saying one can't get past it).

I suppose the main form of treatment would be specialized therapies such as CBT, coherence therapy, writing therapy etc. (there's plenty of info about it at your fingertips online if you're curious), though lots of things can benefit people depending on the circumstances. Effectively addressing the situation in the first place amongst others and coming to terms with it, trying to maintain a realistic perspective thereof and taking cognizance of others' input, listing various accomplishments, positive feedback, success stories and developing a strong support system etc. can help people manage the impostor syndrome at least, and begin to overcome it. Myself, I suffer from clinical depression and have zero self-esteem lol, so treatment, therapy and self-help mechanisms for depression's in a way also helpful for the impostor syndrome feelings; obviously it's still something that I struggle with but I now think it's something I can eventually conquer, and at least in the moment managing more effectively.

A lot of people seem to experience this 'syndrome' at at least some point or another in their lives; just looking at the Wikipedia page I was surprised to see some of the big names (some of whom I'm a big fan of); Chuck Lorre, Neil Gaiman, John Green, Tommy Cooper, Emma Watson, etc. What's additionally interesting to note is that "Some studies suggest that impostor syndrome is particularly common among high-achieving women, while others indicate that men and women are equally affected". Regardless, while it's obviously not ideal that so many people undeservedly undergo it, at least it helps one to relate to others with similar issues and feel less alone and alienated by it. (: