When I was a standard 6 student, my teacher told me about the death of his friend... The friend was young, healthy and happy... he died in his sleep, in bed beside his wife... 

I asked my teacher, "How can people die in their sleep?"... He said that while we're sleeping, our souls would temporarily be released from our body and they would travel to random places... Some souls would travel so far and got lost, not able to find their way back into their bodies... That's why people die in their sleep...

After I heard that, I had quite a number of sleepless nights... Afraid that if I fall asleep, I'll wake up and find myself being in a dark small hole... Buried underground... 

In order to sleep, I would try to think about other things rather than death... I would lie on bed, stare at the ceiling and imagine about how a perfect life would be... How would it be like if I'm rich, tall and handsome... How it would be like if I'm invincible... and other silly stuff... It put me to sleep faster than counting sheep... 

Well, the stuff that my teacher said is just from a spiritual point of view... Here's the scientific explanation on why do some people die in their sleep... According to BBC News, people die in their sleep due to the loss of cells in a particular part of their brain that commands breathing... Click here for more details...

I wish there's a better article on this issue for I would like to know if there's a way to avoid dying in my sleep... The Internet sources are not quite helpful...