Pain In The Back of Head During Workout

I'm 17, I was working out at night and I was lifting some weights but suddenly on my last rep I was pushing myself to hard and I felt a pain in the left-side of my temple. I started getting really dizzy and nausea, I felt like falling over for a few minutes. I was really lightheaded too. That night I stopped working out immediately and tried to relax and go to sleep, but I can't go to sleep at all I've been sweating a lot too during the night. The pain converted to the back left of my head. I went to the hospital and got a CAT Scan but everything came out normal. I feel like my blood circulation in my head isn't working properly. Its really hard to judge what going on because I've never had this feeling before after all the years I've been working out. I am VERY active and can lift heavy weights. I am always hydrated before and after a workout. It's been two days since this occurred and it has not went away. Could it be a tension? Occipital Nerve? Has anyone have an idea whats wrong or when would it go away? I need help asap.