one dream I remember and had several times is one that could be considered a nightmare but strangely enough, I'm really calm when I wake up, as if I knew I was just dreaming.
In that dream I'm already 25 and getting hit by a car and die...
Creepy, I know... But as I say I'm calm when I wake up as if I haven't just seen my death in my sleep.
Anyway. In reality, a dream lasts only a few seconds, even if you have dreamt of a whole lifetime. It's most likely to remember a dream if you've seen it a little before waking up and wake up on your own (not by something or someone else).