Do you have dark thoughts about yourself? Self-hatred, suicidal ideation, that kind of stuff?
In that case, have you tried looking inside yourself for what part of you - which of your inner voices - is the one giving those thoughts?
The usual suspect is an inner critic gone rampant, exaggerating the self-criticism to the absolute extreme. Another part might be in your shadow-self.
In any case, it likely will help to identify that part and give it form, which will allow you to contain it. If it's the shadow, it will very likely flee on it's own, as it doesn't want to be seen at all.