You are starting to reach the early stage of turning, you are lucky you haven't gone through the rest of the change yet, now let's talk about what's been troubling for this long. - Doctor
Transmission & Vectors
This is entirely caused by The Gloom as it feeds off the negativity in the world and will use it to transform those that are trapped by it into creatures of its design.
Negative thoughts and emotions cause the transformation that the person is feeling, and the longer they allow them to remain bottled up and unable to let them go. This will slowly turn them into a Gloomspawn, transforming them into a creature by the very thing that has tormented them, for so long.
Early Stages: The best way to stop the first signs is to talk to the individual about any problems they have been going through and allow them to others. This will gradually keep it from spreading and recede as their problems are mended and are no longer a burden to them. Late Stages: Those who have had prolonged repression of their thoughts and emotions will begin to undergo physical changes as they slowly turn into a Gloomspawn. But a way to stop the complete transformation is to cleanse the corruption with Radiance to burn it away and try to help the individual to let go of the negativity the is turning them into a monster.