what happened???

So this morning, i woke up and i didn’t have a period stain or anything on my sheets. Then, I stand up, I look down a few seconds later, and blood is running down my legs, ALL over me, ALL over the floor. I look at my bedsheets again to make sure i’m not missing anything, nope. they’re 100% clean. What happened? Is that normal? I am kind of new to my period so I don’t have a lot of experience with this.