Miss Lady Professor (2006)

Original title: Miss Jokyōshi

Reiko Mizukami (Akari Hoshino) has finally become the teacher she always dreamed to be. She finds herself always sleepy for unknown reasons, day or night. When she falls asleep in her class, this starts a series of dreams full of erotica to the point where she's unable to discern her dreams and the reality. She has been trapped in an obscene world...