Unprotected sleep is going back to sleep after turning off your alarm clock, risking not waking up for a job, class, or other daily task.

　　英文中回笼觉是unprotected sleep，字面上理解是无保护的睡眠，指的是冒着耽误工作、上课或办事的风险关掉闹钟继续睡觉。

　　It is necessary for someone to have an unprotected sleep after staying up late or working late. It might also be delightful to have an unprotected sleep in weekends or holidays. However, unprotected sleep can be harmful to one’s health as it may disturb your biological clock, resulting in your short memory and blunt responsiveness.

　　在熬夜、加夜班的情况下，睡回笼觉是必要的。周末或假日睡回笼觉也是一件幸福的事情。但睡回笼觉也有可能伤害到你的身体，因为它会扰乱你的生物钟，造成记忆力差、反应迟钝。

　　Example:

　　After twenty minutes of unprotected sleep I missed the bus and had to walk to school.

　　因为睡了20分钟的回笼觉，我错过了班车，只能走去学校。