Hiccup's betrayal

when Hiccup starts doing bad things and destroying berk and endangering inanest people, the hiccup we all love would never do that then why has he now, and the only one that knows that hiccup's the one doing them nobody believes her not even Hiccup himself believes her. what happened to hiccup? why is he destroying berk? It's all up to Astrid to figure it out. warning violent.