A couple of days ago I was trying to take a nap and I was daydreaming and was in a sleepstate. When I was in this daydream/sleepstate I was walking down a corridor. All of a sudden the floor had been lowered and I wasn´t prepared for this at all so I took a step into thin air. I woke up from the daydream and I could still feel it in my right leg, it felt so real! 
This feeling lasted for minutes.
I´m comfused, what happend? 
Moved from General Lucidness. 
Sounds like one of those falling things. They can be pretty intense. It’s pretty common and has happened to me plenty. Sometimes I will feel or even hear a shift in my bed as if I’d reall fallen into my bed! Maybe that’s a really fast shifting of my body as a reponse to it…
That simply sounds like a hypnagogic hallucination. The feeling probably lasted for a few minutes because hypnagogia takes a couple of minutes to wear off.
Probably HI coupled with a Hypnic Jerk.
I got one recently where I was walking down a sidewalk and I suddenly took a step wrong before jerking wide awake in my bed.
You say you were daydreaming, but that sounds like a pretty normal dream to me. There are times when we start of daydreaming and fall asleep in the way, going straight into the dreamworld. Hence the very realistic feeling.
Perhaps, sounds pretty logical. But what about the feeling in my leg that I could feel so intensive? 
Maybe the feeling is similar to the pain you feel after a dream.
Say I get stabbed in my arm in a dream and it HURTS. I might wake up and still feel the pain. You still get this phantom feeling in your leg because of this same mechanism.
… I dunno though.
That never happend to me before, maybe this was the first time? 