Paired Vagus Nerve Stimulation in Mobilization of Patients With Prolonged Disorders of Consciousness

T1: At baseline prior to initiating Phase 1, participants will be assessed using Coma Recovery Scale-Revised (CRS-R), Glasgow Coma Scale (GCS), and Glasgow Outcomes Scale- Extended (GOSE). Following this baseline assessment, participants will continue with 4 weeks of their current standard of care. During Phase 1, no study interventions will be implemented. At completion of T1, the CRS-R, GCS, and GOSE will be reassessed. Following Phase 1, T2a: will be initiated immediately thereby and will entail a 4-week mobilization only phase. Participants will complete 8 sessions of physical therapy over 4 weeks, receiving progressive verticalization and mobilization using a robotic tilt table with robotic stepping (Erigo; Hocoma). T2b: Immediately after 4 week mobilization only period, participants will complete 8 sessions of physical therapy over 4 weeks, receiving the paired taVNS + RTTM intervention. Upon completion of phase 2b, participants will be reassessed with CRS-R, GCS, and GOSE. T3: Following the intervention period, participants will complete three additional study visits for assessment at 3-, 6-, and 12-months post intervention using the CRS-R, GOSE, and GCS. Across all study phases, secondary healthcare utilization, including re-admission rates, number of physicians follow up visits and emergency room visits, will be captured from the patient electronic medical record (EMR) and reported.