Cat, abnormal behavior

Question
My cat has become lathargic.  I have noticed small spots of blood on the carpet.  I am unable to determine the source but I am guessing it is left in spots where he sits down.  He is not eating as much and while he has always been a skinny cat, it appears his weight is falling off.

Answer
Get him to the vet.  There is a good chance that he may have a urinary blockage and is dripping bloody urine.  If that is not it, then there is something else seriously wrong with him that can only be diagnosed by a vet examining him and possibly doing blood tests.