According to my friend, I somehow opened the door for him unknowingly at 2am.
Here goes the story~
Our door, once it is shut close, nobody can open from outside without a key. So in the middle of the night, my friend went out to another room while me and my other friend was asleep.
My friend left and the door appears to be shut when he wanted to come in. He knocked on the door and no one answered. Another friend called my handphone to ask me open the door and I actually picked it up and was talking to him. Next, I actually went to open the door for him when I "heard my friend knocking on the door" and went back to sleep.
The interesting thing is, I never recall doing that last night! Haha!