Why do I feel tired even after a full night's sleep?

Feeling tired despite adequate sleep usually comes down to sleep quality rather than quantity. If you're not reaching deep sleep or REM stages consistently, your body doesn't fully restore itself. Common culprits include sleep apnea, where breathing interruptions prevent deep sleep without you realizing it, alcohol consumption, stress, or an inconsistent sleep schedule that disrupts your circadian rhythm. Other factors include nutritional deficiencies like low iron, vitamin D, or B12, hypothyroidism, dehydration, or depression and anxiety. Even too much sleep can leave you groggy due to sleep inertia. If this is persistent, tracking your sleep with a device or speaking to a doctor about a possible sleep study would be a practical next step.