When I was about 9, i witnessed my mom spank my sister, who was 6. My mom did not hit us and we were generally not punished as kids, but on this occassion, my mother threw my sister over her lap and hit her a few dozen times with her hand.
While seeing this I got an erection and afterwards began fantasizing about what it would be like to be spanked like this. I have replayed this scene of the spanking over and over in my head, and have masturbated to this often. Is this normal?