Study-1 highlights the distributions of a novel sleep biomarker, non-REM hypertonia (NRH), across Parkinsonian Spectrum Disorder (PSD) and non-PSD subtypes. Study-2 demonstrates that NRH is unaffected by SSRI/SNRI use, unlike REM sleep without atonia (RSWA). Study-3 establishes a strong association between abnormal NRH and the clinical diagnosis of isolated REM sleep behavior disorder using RSWA. Study-4 confirms sleep spindle duration as a biomarker for Parkinsonian Spectrum Disorders. Study-5 combines abnormal spindle-duration and NRH as a means to differentiate across and between the PSD vs. the non-PSD subtypes.