The COSP-RBD Study: Concussions and Contact Sports in RBD vs Controls

The goal of this observational study is to investigate concussions and contact sports practices in REM sleep behaviour disorder (RBD). The main questions it aims to answer are: * What is the proportion of patients with RBD that have a history of concussions or exposure to contact sports? * Is this proportion higher to that in control patients without a diagnosis of RBD? Participants will undergo an interview with a sleep medicine specialist to answer questions about history of concussions and contact sports practices. Researchers will compare an RBD group and a control group (without RBD) to see if the proportion of concussions and exposure to contact sports differ.

Inclusion criteria group with RBD: * Patient at the SDC with diagnosis of RBD (Guy's and St Thomas' NHS Foundation Trust). * 50 years of age or above (patients below this age would not be expected to have a RBD related to a synucleinopathy and other causes of RBD would need to be considered instead - e.g. narcolepsy, post-traumatic stress disorder). Inclusion criteria control group: * Patients who have undergone a v-PSG at the SDC (Guy's and St Thomas' NHS Foundation Trust) and who do not have history of suspected RBD or RBD confirmed by v-PSG. * 50 years of age or above This group will be age- and sex-matched to the RBD group. Exclusion criteria group with RBD: * Age \< 50 years of age. * Diagnoses of narcolepsy or post-traumatic stress disorder. * Subjects lacking capacity or literacy. * Non-English speakers. Exclusion criteria control group: * Age \< 50 years of age (in order to match RBD group). * REM sleep without atonia or confirmed RBD on v-PSG. * Diagnosis of neurological diseases, cognitive complaints or motor complaints. * Clinical history suggestive of parasomnia that may be included in the differential of RBD. * Subjects lacking capacity or literacy. * Non-English speakers.