Complex sentence: Chris suddenly wakes up and believes that the encounter with Missy was just a nightmare; however, after a conversation with Walter, he realizes that the encounter was real and that he had been hypnotized to quit smoking.
Split into simpler sentences: Chris suddenly wakes up and believes that the encounter with Missy was just a nightmare. However, after a conversation with Walter, he realizes that the encounter was real and that he had been hypnotized to quit smoking.