Ritalin withdraw????

ok so im on ritalin i do have adhd im not an addict or anything like that so this is how i experience ritalin i take 1 pill after halfhour or so i feel just reallyy good like im all like peaseful and just want pease in the world and i getalittle chatty lol but after like 8 hours or so i feel terrible just horrible my feets will get num and dno just a withdraw.. why is that? and why do i enjoy being on ritalin?