Yes, you can sleep for 8 hours and still feel tired. Even though you got the amount of rest that health experts recommend, you likely woke up toward the end of a sleep cycle. The length of these cycles can vary. We mentioned earlier that a complete cycle could last from 90 to 110 minutes. The duration of each stage can vary too, further affecting the cycle duration. Each person is different, and therefore, you cannot count down a cycle to the exact minute. Instead, these numbers represent a general observation from health experts to help people better understand how we rest.