Have you ever wondered why your head suddenly jerks you awake just at the moment you are about to nod off?

Well experts say it could be because you are stressed, tired or have irregular sleep patterns.

Normal sleep passes through three stages: light slumber, deep slumber and after about an hour the rapid eye movement stage.

But if you're stressed you can go into the REM stage much earlier.

It's here you experience vivid images and dreams but because your muscles are not AS fully relaxed as they should be, you twitch and jerk as if you are moving.

But the good news is - it's perfectly normal and nothing to worry about.