Is there something wrong with me? Do i have a disease?

While at school, i try to avoid any social activities that allows me to speak or communicate. I practically ditched my friends as im so ashamed of this but i do keep in contact via text message + msn (since it doesnt envolve speaking lol). They often ask me "how come your a chatter box on the net but not here?" and my obvious answer to that is ''*shrug* i dunno''. (and i feel so embarred after [;_;] )