I think I may have a concussion?

Today at work I hit my head on a machine, and knocked it pretty good. I have a big knot on my head. I felt fine afterward, but a few hours ago I was in a car wreck and hit my head on the roof of the car really hard. Since then I've been feeling kind of.... dazed, I guess? I feel like I'm dreaming or something. Not to mention my head hurts, my ears are ringing, and I'm extremely tired (granted, I've been awake for almost 24 hours). Could I have a concussion? Is it safe to go to sleep?