If indeed you have lost all that weight then consult a doctor as this much weight loss
is not good that too happening within a week. There are many causes
like worms in stool, depression, anorexia nervosa, AIDS, cancers especially colon cancers, drug abuse, infections and loss of appetite. Loss of appetite can again be due to certain medications, drug abuse, depression, AIDS, acute and chronic infections, cancers and hypothyroidism.