When you wake up at the end of a sleep cycle, you initially feel rested and fresh. If you wake up before a sleep cycle finishes, you’ll probably feel groggy. However, you still get the benefits of that sleep. Here’s how it works: There are 5 stages of brain activity in one sleep cycle. And each cycle lasts about 90–120 minutes. You fall asleep during the earlier stages.
Next, you experience deep, restful sleep. Your heart rate and breathing slow down during these stages, while your body remains still. Your brain is most active during the final sleep stage. As you dream, your eyes move under your eyelids in rapid eye movement (REM). If you wake up during these later stages, you’ll likely feel groggy. You’ll feel more rested waking up at the end of a sleep cycle (ideally in the morning, after several sleep cycles). Or you can feel refreshed waking up after a 20–30 minute nap (before you enter deep sleep).
Sleeping 8–9 hours every day is important—however it happens. And you can shake off any grogginess or “sleep inertia” if you take 15–30 minutes to fully awaken. Standing upright and spending time in light—ideally daylight—can help! As long as you have enough time to fully overcome sleep inertia, you might find that the benefits of a little extra sleep are worth it.
Don’t worry about getting enough deep sleep or REM sleep. Trust your body! It has an amazing ability to recuperate when you catch up on sleep. And it will quickly fall into whatever stage of sleep you need most.