Abstract Introduction Narcolepsy with Cataplexy is a central disorder of hypersomnia that is characterized by excessive daytime sleepiness and Rapid eye movement (REM) dissociation phenomena. A common manifestation of narcolepsy is REM behavioral disorder (RBD), a parasomnia characterized by loss of muscle atonia during REM sleep (RSWA). While RBD is relatively common in patients with narcolepsy, very extreme movements are considered rare. Report of Cases: A 20-year-old male with no significant past medical history presented with 8 months of new onset daytime sleepiness, sleep paralysis, and auditory hallucinations at sleep onset. After initial evaluation at our sleep center, he was scheduled for actigraphy testing and sleep logs, followed by video polysomnogram and mean sleep latency testing (MSLT). Initial PSG results were notable for a total sleep time of 498 minutes, a normal apnea-hypopnea index of 0.7/hr., sleep onset latency of 0 minutes, and REM latency of 0 minutes. Based upon military medical standards, the MSLT scheduled for the following morning was cancelled due to limited sleep during the preceding 2 weeks as measured via actigraphy. However, the patient’s sleep logs reported over 7.5 hours of sleep per night. The patient’s video PSG was reviewed, which showed evidence of frank RSWA, as well as episodes of dream enactment behavior during REM sleep, all including very violent movement in his upper extremities. Repeat trial of MSLT 2 weeks later showed mean sleep latency of 1.7 minutes, with 5 sleep onset REM periods (SOREMPS), and evidence of dream enactment involving the upper extremities during 3 of these SOREMPS. Conclusion We present the case of a patient with narcolepsy and RBD with significant upper extremity movements to the point of affecting the actigraphy sleep/wake detection algorithm. Actigraphy has been validated as a diagnostic tool in assessing sleep and wake patterns in individuals without significant REM sleep dissociation phenomena; however, our case highlights the necessity of further research of the validity of actigraphy in patients with Narcolepsy and/or REM behavioral disorder. Support (If Any)