或許每個人都有過這種經歷，在熟睡的時候，突然感覺失重，從很高的地方往下掉，伴隨著身體四肢的抽搐，雖然我們的身體已處於休眠狀態，但我們還是能意識到自己的身體抽搐了一下。小時候，大人們告訴我們，這種情況是在長身體。其實不然，這樣的情況，大人和小孩都可能會遇到。那麼究竟是什麼原因導致的這種情況呢？
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醫學上是這樣解釋的，睡覺時突然感覺下墜，一般是發生了臨睡肌躍症，又稱為肌抽躍症。這不是一種疾病，70%的正常人群都會出現這種情況，這種情況發生的原因往往和患者過度疲勞或者不正確的睡姿，以及缺鈣等有關係。這種情況往往發生在患者剛剛入睡或者快要醒來時，患者的高階神經功能處於抑制狀態，失去了對低階中樞的抑制作用，導致低階中樞接受輕微的刺激就會出現過度活躍，引起肌肉收縮。患者往往會出現睡眠中的下墜感或者肢體抖動，將患者驚醒，不需要特殊治療，如果太過頻繁發作，需要明確有無焦慮症。
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簡單點說就是，人們在睡覺的時候心率會降低，當心率降低到非常低的時候，大腦檢測到異常，為了確認你還活著，開啟了保護機制，發出刺激訊號，將你驚醒。如果遇到這種情況，不要慌張，保持身心舒暢，規律作息，堅持鍛鍊。這樣的症狀自然會消除。
Maybe everyone has experienced this kind of experience. When we are sleeping, we suddenly feel weightless and fall from a high place. With the convulsions of our limbs, although our body is in a dormant state, we can still realize that our body has twitched for a while. When we were children, adults told us that this situation is growing body. In fact, it is not. Adults and children may encounter this situation. So what is the cause of this situation?
Medical interpretation is like this, sleep suddenly feel down, is generally the occurrence of nocturnal muscle jump, also known as muscle jerk disease. This is not a disease, 70% of the normal population will have this situation, the reason for this situation is often related to the patient's excessive fatigue or incorrect sleeping position, as well as calcium deficiency. This kind of situation often occurs when the patient just falls asleep or is about to wake up, the patient's high-level nerve function is in the inhibition state, loses the inhibitory effect on the low-level central nervous system, leading to the low-level center receiving slight stimulation, which will lead to overactivity and muscle contraction. Patients often have a sense of falling in sleep or limb shaking, will wake up patients, do not need special treatment, if too frequent attacks, need to determine whether there is anxiety.
To put it simply, people's heart rate drops while they sleep, and when the heart rate drops to a very low level, the brain detects abnormalities, and in order to make sure you're alive, it turns on the protection mechanism, sends out stimulus signals, and wakes you up. If you encounter this situation, don't panic, keep your body and mind comfortable, work and rest regularly, and keep exercising. Such symptoms will naturally disappear.
參考資料：百度百科，知乎
翻譯：Google翻譯