This is almost the same thing that happened to me...almost.
For the last year straight i've tried almost everynight to WILD or atleast have a 5 second lucid...and only suceeded in having 5, three were between 10-15 seconds long, and the last and most recent being around 10 minutes.
So the last couple of months have been so frustrating, and in the middle of an attempt at WILD one night I snapped and said F($%*$#(%* It.
I got tired of trying, and at that point and attitude I was sick and tired of trying to attain lucidity for good.
I said "Screw it, tomorrow I'm throwing my books away and giving up, this is getting too frustrating" (I know,what a pessimistic attitude right?)..Anyways, I said this outloud and firmly meant it and went to sleep. About 4 hours later I realize i'm dreaming, three times in a row.
You could try the "I dont care so much that the last thing on my mind before I go to sleep is dreaming" whether its angry or not, which I suppose is a form of Autosuggestion.
Update your dreamsigns frequently..I see alot of dreamsigns that occur frequently in almost everyones dreams, but I find the dreamsign that works almost 100% of the time for me is the sun.
Most people sleep during the night anyways right?
So if you're going to bed, whats the most obvious thing you're not going to see? The Sun.
If you do, you're dreaming.
Obviously this won't work for naps in the afternoon, then vice versa..look for the moon.
Last one here, because this one helps me recognize i'm dreaming and stabilize.
Watch a scary movie before bed,(preferably more then one to get the juices flowing..no pun intended.)
Go to bed scared. Look up ghost photos, read some ghost stories,etc.
Fall asleep-->REM-->Dreams(or in this,nightmares)--> instantly lucidity when Jason Vorhees comes out of the woods with a machete...he's not real, you're waiting for a nightmare since you went to be spooked...Bam, instant lucidity when you realize an imaginary killer is chasing you through a cornfield.
All it takes a little belief and a loose awareness..React, don't expect.

I'm sorry if i happened to roll off topic somewhere I'm just trying to relate and help out.
I hope this helps, if not then i'm sorry for takin your time!
-JF