I tried meditation for the first time, and i got scared? wtf?

I just sat in the middle of a dark room, legs crossed, back straight. Doing nothing but breathing for several minutes. Then I suddenly got this weird feeling like I was slipping away from the earth. My breathing also started to feel like nothing. I felt weightless, and I felt like I was fading away in to nothingness. I have never experienced a sensation like this in my life. This actually surprised me, so I fought it. When I opened my eyes, my heart was beating really fast and my palms were sweaty. What do you think happened? By the way, I'm a 15 year old male.