Sentence:  "<WSD>Pronoia</WSD>" is comparable to paranoia (which is commonly believed to be a mental disease), but is its emotional opposite. The paranoic thinks that everyone and everything are conspiring against him. So-called pronoids see reality as quite positive, and regard themselves as responsible for good things, which they are convinced are going to happen. If paranoia is a mental disorder, then <WSD>pronoia</WSD> is a mental disorder. So (apparently) happiness is a mental disorder. 
Meaning of the word marked with <WSD> tags:  A belief (sometimes regarded as irrational) that people conspire to do one good. (from 1981)