Dreams that end in dying!

[The Moon]

I was wondering if someone could help me with my friend's nightmares. I do not know much about nightmares. But my friend's nightmares seem kind of alarming and I would like to find out their meaning. These are the details I have on the nightmares (keeping in mind that my friend reads a lot of scary books and such): He says he has these almost every night. Each one is different, but in the end he always ends up dying. He says that they start out where everything is going great for him and he's happy then something comes along and ruins it. For example: He was dreaming that he was flying. Just enjying himself when suddenly the army comes and shoots him down. Do these dreams mean anything? Can they be categorized like other Nightmares?