skip to content skip to search skip to navigation Listen Live skip to logon
Tuesday 1st September 2015
Max 18°C | Min 13°C

Why does our leg jerk just as we're going to sleep?


sleep.jpgI hurt my knee yesterday and it hurts when I am just getting to sleep and then my leg spasms. Why does that happen?
Matt, Acton


** Joint-definitive **
Name: Stuart, near the London Eye
Qualification: I watch House a lot
Answer: Itís known as a Myoclonus reaction, which is what happens when  your blood pressure drops Ė due to a decrease in brain activity - so much that your brain panics and thinks that your heart has stopped, so it sends a bolt of adrenaline to your heart, which is what causes that jerk reaction when youíre asleep.
(James OíBrien: I canít give you a round of applause for it as I donít know how medically accurate House is. It sounds good, but we need more proof on the blood pressure bit.)

** Joint-definitive **
Name: Lawrence, London
Qualification: Doctor
Answer: I hate to argue with Hugh Laurie, but I think thatís wrong.  Itís known as a hypnagogic event, due to a disorder. Normally when we fall asleep, the part of the brain that controls the muscles and movement switches off, which prevents us from acting out our dreams. But in some cases, that doesnít happen for a while, so you get movement when youíre falling asleep.
(James OíBrien: Is it possible that both you and Stuart are right?)

Do you agree? If you know the answer, write it in the box belowÖ