WHY can fatigue "attack" after an afternoon nap?
This kind of sleep doesn't always help you wake up. It's all about "sleep inertia," that is, the transition from sleep to wakefulness. "The longer you sleep, the more likely you are to 'fall' into deeper phases of sleep," explains Dr. Dawn Dor-Stites of the Sleep Disorders Center at the Michigan Medical Center.
"Waking up in the wrong phase can lead to sleepiness and irritability. Limiting daytime sleep to 20 minutes is key, so you'll wake up rested."
The exception to this is when you have enough time to take a nap during the entire sleep cycle, which lasts about 90 to 120 minutes.
