What Was The Episode Of Dizziness After I Banged My Knee?

Hi there. I am 43 years old. I was at my Mothers and went to sit cross legged on the kitchen chair to read a book. I smashed my left knee cap on the corner of the kitchen table leg. I got very very dizzy so I put my head down on my arm on the table. Next thing I know I'm waking up on the floor with my Mom yelling for my Dad to call 911. I thought I was going to vomit. This happened once before about 20 years ago when I banged my knee. I was tested for epilepsy because I had minor convulsions back then and I guess I did this time as well. Mom said I was white as a ghost. I didn't go to the hospital because I do get dizzy when I bang my knee but I don't usually pass out !! Any idea what could cause this ??