There are many ways to purposely wake yourself up from a LD. I guess each person has their own way...
personally, this has always worked for me: simply close your eyes really tight, and then sloooowly open them up. When they are fully open, you should be looking at your bedroom, at the real world (i.e you should be awake&#33 It's never failed me yet, give it a shot.
Hope this helps some.