I hit my head hard? Possible concussion?

Earlier today I hit my head really hard on the wall. I was about to sit down on the couch when I just let my body go and I hit my head and my head flew forward. I did not black out but almost right afterward I felt a little bit weird. I got really sleepy and I felt confused. Now 4 hours later I am feeling a lot better but my neck kinda hurts and every time I stand up my head hurts a lot and I feel dizzy. that's what really bothers me... Could it be a concussion? or is my head just a little sore from hitting the wall?