Okay, so the other day I was sitting in my den, reading when I suddenly felt this weird, painful feeling in the middle of my head, like, deep inside it-- the only way I can really describe it is like a tiny popcorn kernel popping in the center of my brain. I also tasted copper in my mouth for awhile... After that, my head hurt for about a minute, not intensely but I had difficulty concentrating and there was a cold feeling in the back of my neck then it vanished.

It's happened about three times since then, does anyone know what this is? I couldn't find anything online.