Thanks very much everyone, It's nice to know that he's probably just a normal 2, almost 3 year old kid. I was really worried knowing that he would go to such lengths in a tantrum as to hurt himself and not notice.

Shezbut, I do let him wear his PJ's all day. The problem arises when his older sister gets dressed. He will say he wants to get dressed too, then change his mind when I try to dress him. Then change his mind again when I agree to let him stay in his PJ's. I just don't know if this is normal for kids to change their minds just to stay being mad.
He's getting what he wanted, but he still changes his mind. I don't know if he does it to anger me, because he likes confrontation, or because he figures it's some sort of game to play.
Thank-you for all the suggestions.

Jimi I know he's his own person. I am not trying to change who he is and in fact I try to let him be himself all the time. I let him make decisions on what he would to wear, eat, do, play etc every day. The only thing I'm trying to change about him is his constant need to flip flop on what he wants, and his destructive and self-harming behaviour.
I know slapping him was wrong and I immediately regretted doing so. I feel like an awful mother for doing it and I'm sure I'm going to regret my mistake for the rest of my life.

healinginme4me; time out worked so wonderfully with my first daughter. She would sit patiently and calm down in no time. I tried it with my son when he was a little over 1 and it never seemed to work. I could spend forever trying to get him to stay in time out and he would just keep screaming/kicking and running off that I gave up.
I can assure you he is very high-strung. He has energy up the wazoo and from what my MIL tells me, his dad was the exact same way (he was also the middle of 3 kids) She told me he gave her so much trouble that seeing my son act like he does takes her back to when my husband was 3.
If he continues to be like my husband was as a child, he'll finally calm down around his late 20's LOL

Thanks again guys for listening to my rant.