hypnic jerk

Noun

An involuntary twitch which occurs just as a person is beginning to fall asleep, often causing momentary wakefulness.

Japanese Meaning

入眠直前に起こる、不随意の筋肉の痙攣（瞬間的な意識の覚醒を伴うことがある） / 眠りに落ちかける際に発生する突然の筋肉反応

I was almost asleep when a sudden hypnic jerk startled me awake, making me jump and check the time.

もうすぐ眠りにつくところで、入眠時に起こる不随意なけいれんに驚いてはっと目が覚め、飛び上がって時計を確認してしまった。

Sense（1）

An involuntary twitch which occurs just as a person is beginning to fall asleep, often causing momentary wakefulness.

hypnic jerks

（ plural ）