The Best Way to Nap
A study published in the journal Heart found a link between healthy napping （打盹）and a lowered risk of heart disease. The American Psychological Association points out that naps can improve memory, learning capacity and mood. Sara Med nick, PhD, a neuroscience at the University of California explains that when you fall asleep, your body moves through stages that each play a role in health. Ideal napping times are based around this four-stage cycle.
| Stage 1 | The "dozing off"（打瞌睡）period |
| Stage 2 | muscles, heart rate and brain activity slow down |
| Stage 3 | deep, restorative sleep |
| Stage 4 | REM(rapid eye movement)sleep, when brain activity increases and you're most likely to dream |
| The 20-minute nap | Between 20 and 30 minutes is one napping sweet spot, according to Mednick, who explains that you get enough Stage 2 sleep to switch your body and mind into full relaxation mode, aiding with memory. |
| The 60-minute nap | Stage 3 sleep is a time for your body to repair tissue, strengthen the immune（免疫）system and recharge energy stores. But waking up during this phase can make you feel uncomfortable and sleepy, Med nick says. Most people start to move out of Stage 3 after around 60 minutes, which makes it a good time to set your alarm. |
| The 90-minute nap | A complete sleep cycle is about an hour and a half, and napping for a full cycle can have big benefits. But naps longer than 90 minutes can disturb nighttime sleep and might even weaken memory. |
Not a regular napper? That's OK. " Everyone needs to rest, but not everyone necessarily needs to nap," says Med nick.
