Doubt that your work is good enough for anyone or anything. Shouting into a void. Impostor syndrome.
They're very familiar to a freelance journalist, and novelists not only aren't immune, they probably get it worse, because they've poured everything they have onto those pages and the words on them represent their very soul.
After slaving over something you consider so important and being proud because you feel you got it perfectly right, you might get a quick email from your editor saying 'thanks' – sometimes not even that – and then your words and ideas go out into the world and disappear, giving you no indication of whether they ever have any impact on anyone.
I've barely started marketing Falling by trying to get it in the hands of people who can sing its praises to a wider audience, and (as the physics of celebrity always imposes), the bigger the name, the less likely they are to even read what I've written, let alone care about it or talk it up to anyone.
Many of them are writers or producers themselves, after all, and have their own projects they're trying to shill. They probably barely have time to read email. Who the hell's going to read a 260,000 page genre novel?
Fear of and certainty of failure are biting hard right now.