South Korean cinema continues to be a thriller forerunner in many genres, especially horror, and the new horror thriller, “Sleep,” seems to be continuing the tradition. The film is the feature-length directorial debut of Jason Yu, a second unit director on Bong Joon-Ho’s sci-fi-ish thriller “Okja.” The connections to Joon-Ho don’t end there either, as “Parasite” star Lee Sun-Kyun is among the cast members.