Phase IIB 2-Period Crossover Polysomnography Study in Participants With Primary Insomnia (MK-4305-006)

Inclusion Criteria: * Has a diagnosis of Primary Insomnia based on sleep history and the investigator's judgment * Must be willing to stay overnight at a sleep laboratory * Must be willing to stay in bed for at least 8 hours each night while at the sleep laboratory * Regular bedtime is between 9 PM and 12 AM (midnight) Exclusion Criteria: * Breast feeding, pregnant or planning to become pregnant during the study * Within the past 6 months before starting the study you have a history of significant cardiovascular disorder such as unstable angina, congestive heart - failure or acute coronary syndrome * Currently participating or have participated in a study with an investigational compound or device within the last 30 days * Has traveled across 3 or more time zones in the last 2 weeks or plans on traveling across 3 or more time zones at any time during the study * Has done shift work within the past 2 weeks * Has donated blood products within the last 8 weeks * Has difficulty sleeping due to a medical condition