Weird period stuff, has never happened before

So it was the forth day of my period. And I was hit this massive crazy never before experienced cramp. I was in the middle of typing a reasurch paper in the computer lab, lots of people, and all I could do was sit with my head in my hands and repeat to myself that it would go away.

I'm Also very regular and have a pretty average flow, completely textbook period. I also 18 and am a virgen. No sex ever. Zip no nadda

So I get up and practically stumble to the bathroom, and this GIANT clot thing is there. I've had some small ones before but this one was what I imagine close to the size of my uterous. Afterward I had to go to the nurses office cause I got shakey and it was hard to focus.

Is this normal and is it life threatening?? Please help??