Background: Severe SARS-CoV-2 infection often results in prolonged immobilization and intensive care unit–acquired weakness (ICUAW), contributing to delayed functional recovery. Early physical and rehabilitation medicine (PRM) interventions may mitigate neuromuscular decline, yet real-world data integrating kinesitherapy with proprioceptive focal stimulation (PFS) remain limited. This study evaluated the functional impact of early rehabilitation and the role of timing in rehabilitation among critically ill COVID-19 patients. Methods: A transversal observational cohort study included 148 adults with confirmed COVID-19 admitted to the ICU of the National Institute for Infectious Diseases “Prof. Dr. Matei Balș” (June 2020–June 2022). Individualized rehabilitation (kinesitherapy ± PFS) was initiated after hemodynamic stabilization. Outcomes included the Medical Research Council score, the ICU Mobility Scale, the Manchester Mobility Score, and the Glasgow Coma Scale. Statistical analyses used the chi-square, Mann–Whitney U, and Spearman's rank correlation tests. Results: One hundred and eight patients (73.0%) required mechanical ventilation. Intubation was strongly associated with muscular atrophy (p = 7.1×10⁻¹⁰) and lower ICU mobility (p = 1.56×10⁻¹¹). Delayed rehabilitation correlated moderately with poorer mobility at ICU discharge (ρ = −0.397). Conclusion: Early PRM is feasible and associated with better functional outcomes in severe COVID-19. Rehabilitation timing appears critical, particularly in mechanically ventilated patients.