An incubus is someone or something that really drags you down, like a so-called friend who only calls you to complain about her life or a job that you can't stand.
Incubus comes from the Latin word incubo, meaning "nightmare, one who lies down on (the sleeper)," which describes an evil spirit that crushes people in their sleep, triggering terrible nightmares and making them feel like they're suffocating. In the Middle Ages, not only did people believe incubi (yes, that's the plural) were real, they passed laws against these terrifying spirits.
