I gnash my teeth while asleep.
Seriously go get an occlusal guard. I went for a long time without one due to not having insurance/not having spare cash, and now due to the grinding I have a tooth that was fractured above the gumline that became infected. They had to slice a flap in my gums to get to the damaged region, then because the damage was so progressed it required a root canal which was the worst experience of my life due to the tooth being "hot" (read: It was numbed properly but I could still feel all the work being done). All this even after I meticulously care for my teeth on a twice-a-day regiment. It's frustrating.