To make sure you don't wake up groggy after a nap either stick to a short 20-minute nap or a longer nap of at least 1 hour and 30 minutes.

为了确保睡醒后不会有迷迷糊糊的感觉，要么坚持一个二十分钟的短睡眠，要么一个至少一个半小时的长睡眠。