I can't remember that I'm in a lucid dream?

Yes, the title is strange, but in the two lucid deams I've had, I'v realized I was lucid, tried to do something, (it was fly in my first dream but I fell flat on my face. In my dream last night it was try to materialize someone infront of me.) When this didn't work, I'd just "forget" I was in a lucid dream.

Let me provide an example, because I know it's confusing:
First Lucid Dream: I walk down some stairs and notice that they are "strange" like an optical illusion. I freak out and am so happy to have my first lucid dream that I almost wake up, but I spin in a circle to go back into deep sleep. Then I run down the hall to try and fly, I jump in the air, lean horizontally, and fall flat on my face. I get up and am wondering why it didn't work. I walk over to one of my old teachers, then the dream continues like I was never lucid, I forgot that I was in a dream!

Last Night: I was hitting on a girl I really like at school, as practice for when we get back in school. We play some dodgeball/kickball game. Then I'm walking in my mansion and I realize, "WAIT! I'M DREAMING!" I can't remember what made me think that though. I think, "Ok, I can't fly right now, so lets try materializing Paige". I try to materialize her (the one that I like) and sort of see her, but she is extremely transparent and not very stable, like I'm imagining her while awake. I realize that I can't materialize her, and walk out out of the room to a window. I look out the window to see if I could make the sky change colors. I look out and see and Hannah (a girl that I'm good friends with) and some other people. She sees me and looks angry. At that point I forget that I'm dreaming and the dream continues like I had never been lucid at all. I had forgotten I was in a dream.

If this will help, I was using the DILD method.

You lost lucidity, it's common if you aren't focused and happens to everyone. Set up a goal and really feel like accomplishing it might help. Also RC alot and tell yourself you're dreaming. If you really want to remember the entire dream and don't lose your lucidity, try waking yourself up when the goal has been done. Other than that, I just think it's something which will pass. You don't have to worry :) Good luck!

Yes, as Matte, said, this is actually pretty comon. It seems that in dreams your mind becomes distracted fairly easily. As the dream goes on, you need to keep reinforcing your lucidity by performing RC's and reminding yourself that you're dreaming. The need for this seems to become less with experience, but it's always important to keep it fresh in your mind (this also seems to improve control and often vividness for me).

It happends to me all of the time, it is common. Nothing to worry about, take supernova and matte87s advice.

Thanks for the advice, I'll see how I fair tonight.