Replacement Naps are taken to make up for previous sleep loss. These naps should be long to ensure the restorative powers of a complete sleep cycle. For example, if you are sleep deprived and you feel tired, a longer nap of about 90 minutes may be appropriate. A 90 minute nap means that you will likely go through an entire sleep cycle. Sleeping for an entire sleep cycle will help you feel refreshed and more alert, while also ensuring that you do not awaken in deep sleep.