In the initial stages of sleep, your heart rate and breathing slow down quickly.
But sometimes when someone is extremely exhausted, the brain proceeds through this stage of sleep too quickly and it actually confuses the brain into thinking that you are dying and that systems are failing.
The body quickly responds with a jolt of chemicals that make you slam awake.
This is the working theory of the "hypnic jerk". Indeed, this is only a theory at the moment and more research will need to be done to confirm this.
Another mystery concerns the visual perception of falling that we experience in our dreams just before we wake up.
One possibility is that the parts of the brain working dream creation may be trying to make sense of the sudden need to wake up, and as a result, a likely dream scenario is created.
COMMENT on Facebook to let us know if you have ever experienced the "hypnic jerk" and why YOU think it might be happening.