Sleep deprivation and oversleeping both carry significant health risks, though they involve different biological pathways and outcomes. Animal studies demonstrate that severe sleep deprivation is lethal, primarily through the accumulation of reactive oxygen species in the digestive system rather than through direct effects on the brain. While reported human deaths from sleep deprivation remain very rare (if any) outside of specific genetic conditions (e.g., fatal familial insomnia), extended sleep loss creates measurable biological damage. On the other hand, regularly sleeping more than 9–10 hours is linked to a higher risk of metabolic and cardiovascular problems. However, oversleeping is often a symptom of an underlying health condition such as depression, metabolic or thyroid disorders. Understanding how bot too little and too much sleep affect the body is essential for recognizing and managing sleep-related health risks.