I had a very rapid heart beat for a few seconds, which went to my brain and I felt pressure, almost as if some one was inside my skull pushing down, became very dizzy, which gave me a severe headache. That lasted about 10 min. I had the shakes for a bit after the heart rate slowed down. It was all I could do to keep from passing out. While I was dizzy, the room kept going dark. I fought it until it was over. Is this normal?