We've all been there, in the space between sort of awake and almost asleep when we feel a jerking or twitching within our body. Sometimes the movement can be so strong that it kicks out a leg. Why does this happen?

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We recently had a horrendous wave of nasty thunderstorms roll through and my six-year-old son woke me to ask if he could climb into bed with me and if I would hold him until the storms passed.

As I held my son in my arms and heard his breath slowing, I felt relief because I'd been afraid that the intensity of the storms would prevent him from falling asleep, but the slowed breathing indicated to me that he was almost in dreamland. And then, his little body twitched.

My son has had involuntary twitches from time to time as his little self falls asleep since he was a newborn so I wasn't alarmed when his foot met my shin, but I did find myself curious. Sometimes I'll be almost to the sleep realm when I'll feel a twitch and I've felt the same from my husband. Why does this happen?

As it turns out, these little twitching or jerking movements are called hypnic jerks and there's a theory that they happen when our muscles relax for sleep but our brains haven't made the connection that's what we're up and thinks maybe we're falling so it tries to kick out muscles back into gear.

Pretty cool, right? By the way, doctors say that hypnic jerks are totally harmless and that they happen to everyone.

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