RecruitingBehavioural interventionBehavioral Treatment for Nightmares in REM Sleep Behavior DisorderThe purpose of this clinical trial is learn whether a behavioral (non-medication) treatment can reduce nightmares in adults with Rapid Eye Movement (REM) Sleep Behavior Disorder (RBD). People with RBD will be enrolled in the study along with their family members (a partner or other family member residing in the same home). All participants will receive the treatment via videoconference and will complete 2 assessments. Participants with RBD will attend 7 sessions, and their family members will attend 2 of those sessions with them.