Please take your cat to the vet ASAP. His symptoms could by due to many serious illnesses such as a urinary blockage from a urinary tract infection or Feline Urologic Syndrome, a traumatic injury, pancreatitis, and many others.
oh i forgot to mention that he is eating still but i have no idea whether or not he is drinking or using the bathroom!!! and my other cat [female, age 4] definitely notices somethings different because she sits in front of him alot and seems concerned about him!!!!!