Is it only during REM sleep that the body repairs itself?

No, the body repairs itself during various stages of sleep, not just REM sleep. While REM sleep is important for brain function and memory consolidation, other stages, particularly deep sleep (slow-wave sleep), are crucial for physical restoration, muscle growth, and tissue repair. Hormones like growth hormone are released during deep sleep, facilitating these restorative processes. Thus, all stages of sleep contribute to overall bodily repair and recovery.