For me it's just how my body feels. In a dream everything is lighter and moving my body quickly however I want is easy. I like to do things like run on all fours or hop really far.

I had a few lucid dreams growing up but my constant nightmares really kicked me into lucid dreaming every night. One night I just got sick of how scared I was and stated fighting back with whatever power I could manage. Now I can control most things fairly easily.