What's wrong with me?

I am a 15 year old girl, about five ft three, and about 110 pounds. I used to be all into running, but I haven't done it in about a year. I decided to get back into it so this morning I woke up, at some raisin bran and went out for a jog. I had only done about 1/2 a mile and my arms started to feel really heavy, and I felt dizzy and weak and started to black out. Not just like I was tired cause I was out of shape, but like I was going to p out. What's the matter?