Why does my alarm clock create cliffhangers?

This morning I was having a beautiful dream. I mean REALLY beautiful - the kind you only have rarely, and that stay with you into the day. I wasn't in the dream; it was a love story that played out for me watching it like a movie. The man and the woman were brunette and lovely, there was piano music playing throughout, and the scenes were gauzy, filtered and sepia-toned (have I been too much on the Instagram maybe?). I won't bore you with details (too late?!) but believe me when I say this particular dream was something special -beautiful, haunting, lyrical, and different. It was the New York Times critical review best seller of dreams.

Seriously, I know it's just synapses firing in our heads and our memories, plans, hopes, fears and various daily influences sorting themselves out into their little filing cabinets - but every now and then our brains produce something wonderful in a dream.

These rare, lovely dreams seem to come from nowhere. I can't pick what influenced this one, nothing I was reading or thinking or seeing the past few days explains it.

And here's the other thing that seems to happen. My alarm clock woke me up RIGHT at the pivotal point in the story - the make or break scene on which the whole story was hanging. I woke up with that weird dumb feeling you get like "Oh no! I want to know what happens!" Like it's a movie on TV instead of something your own imagination has produced.
Then you spend the next few minutes trying to work out how it would have ended, which is really quite weird when you're the one who has created it.

But what I'm wondering is this: WHY does this happen? How does my alarm clock go off right at the pivotal moment? This is not the first time this has happened - I might as well dream of a murder mystery with the victim gasping "The murderer is..." right as my alarm rings.

I think my mind is somehow, subconsciously, doing this to me on purpose. I have a theory that my mind takes tiny cues from outside my bed (the light out the window, the little click the clock makes before the alarm goes off), and sets up a storyline it can't possibly wrap up, "knowing" it doesn't have to finish the story...
But HOW does it do this? How does it get the timing just right?

Alternative explanations: selective memory (I'm not remembering the times this doesn't happen); or perhaps I am imbuing the dream with more significance because of the interrupted ending, or I am not remembering it correctly... Or the dream was not as amazing as it seemed and the lack of ending means nothing...

"Sommeil d'hysterique" from Bibliotheque
de Toulouse, via Flickr CC

Does this happen to you? Do you have "cliffhanger" dreams? 

How do you interpret them?