Wake Up Refreshed: The Science of Sleep Cycles and Avoiding Sleep Inertia

Feeling groggy after a full night's sleep? Many people experience this common problem. The reason, according to Dr. Joe, MD, a US-based ER doctor, is that waking up during the deep sleep phase leads to sleep inertia. In a recent TikTok video, Dr. Joe explains that our bodies progress through different sleep stages in 90-minute cycles. Waking up during deep sleep, which is crucial for restorative processes, leaves us feeling tired and groggy. To avoid this, Dr. Joe recommends aiming for wake-up times that coincide with the end of a sleep cycle. This means sleeping in 90-minute increments, such as 6, 7.5, or 9 hours. He also suggests limiting naps to 30-40 minutes to avoid entering deep sleep. By understanding and aligning our sleep with these cycles, we can wake up feeling much more refreshed. "It’s not just about how long you sleep—it’s about when you wake up," says Dr. Joe. His simple advice offers a practical solution to a widespread issue.