Whenever my cat goes to sleep,after a minute or so, it turns upside down (belly up)and there is some twitching in the paws legs tail and whiskers. Is it normal or some disease?
Some people prefer to sleep on their stomachs, others on their sides or backs; some change position depending on how warm or cold they are or for other reasons.
The same is true of cats. Upside down may look silly to us, but it really doesn't mean anything but that the cat is comfortable that way, and that it trusts you not to try to take advantage of this less-defended pose.
A bit of twitching of paws and face usually just indicates that the cat is dreaming.