Hey Visceral,
Well, if you know for sure you were awake (and not experiencing a moment of false awakening), then I'd say it could also be that the nightmare itself raised your level of excitement to the point of consciousness - waking up.

In the past I think I sorta "knew" i was dreaming [/b]
The basic question regarding whether you were lucid really comes down to whether you remember actually saying to yourself "I am dreaming" or "this is a dream". There's really no "sorta" - it's mostly a matter of remembering (recall). I believe we ALL go through this lucid stage every night both on our way into sleep then back up out of it. It's just part of the process. Yet, we hardly ever remember it (and it's likely we don't spend enough time in this state - we just go right on to waking up).

To improve on this, you should work on your dream recall - and that starts with keeping a dream journal and training yourself to remember your dreams.