It's possible that Hōtarō has a minor mental disorder known as psychosis due to his "loss of contact to reality". There's some proof that he has that kind of condition, for example, when Chitanda asked about her curiosity to Hōtarō on Episode 6, Hōtarō suddenly hallucinates a group of Chibi-sized Chitanda Angels saying "Watashi Kirinarimasu(lit. "I'm Curious" in Japanese)" almost covering his whole body. Aside from hallucinations, the one who suffered Psychosis is also prone in many different ways, like difficulty to have a social relationship to someone(which explains why Hōtarō is an Introvert and has known only few friends), unusual or bizarre behavior, and impairment in carrying out daily life activities(which explains why he's lazy most of the time).