Question about how to get your child to listen..

Have any of you gotten a root canal? Yesterday was my first time getting a root canal and I got 2 done. I waited so long and tried putting it off but my face was swollen and i was in so much pain that I had no choice but to get it done! I'm glad I got both done at once but I'm hurting. My son likes to hit and head-butt so I've had to watch out. It's been stressful trying to manage him and myself today which brings me to ask.. How do you get your child to listen? He knows what NO means but chooses to laugh at me and continue doing whatever it is he's doing. I've tried slapping the hand after saying no multiple times. He is only 13 months old, but he knows his limits. I read in a magazine to not disipline until 18 months but I feel like he'll be so much worse then! He hates being told what to do! In the mall I let him walk if he's been in his stroller for too long.. but he doesn't want to hold my hand he wants to roam, so I let him but I have to guide him so he doesn't go into EVERY store. When I grab his hand to turn him he drops to the ground, dead weight, and screams and kicks! I feel like I have THAT KID. Ya know.. the one in the grocery store screaming like a maniac and everyones staring and finds them hitting their parent and screaming and kicking. I just am wondering how do you prevent that?