I am 27 and it happens to me since when I was a teenager. It happens once per month on average; sometimes more, sometimes less. It's the most horrible thing I can experience. It only lasts a couple of seconds, I think that if it lasted longer I would pass out or have a heart attack, I don't think I could bear that suffering.   I will describe it below:   It occurs always 45 minutes after I have fallen asleep. I guess I am in a point between daydreaming and deep sleep and my mind is very very clear. I suddenly realize that I am going to die someday, that there is no a single change I can´t avoid death; I am gonna die and all "my world" is gonna dissapear. I mean, I can think about the death during the day and nothing happens, it is just a though, but this time I 100% realize it. Then I wake up screaming like fucking crazy (it is a horrible scream, very high pitched and with a high volume) and shaking, I can´t controll it. This experience last 1-3 seconds but it is the most horrible thing you can imagine. What make it so scary is that it is fucking real.   I am not so concerned about the experience itself, because it only lasts a couple of seconds, but these things worry me:  I wake up and scare my whole family and all the neighbors on my block with the scream. There are children who are scared and cry in the apartment below. I feel really bad about this...   Maybe one day when I get an outbreak of these I could have a heart attack, because I go from being calm to being in a panic mode like lightning.