I have a cat that unfortunately had to have his front right leg amputated.  This was due to Vaccine related Myxsosarcoma (High Grade).  Margins came back 2cm clean.  His name is Bruster and 10 years old.  Bruster until the amputation acted like a dog, followed me around, extremely friendly.  He could be on the somewhat startled side at times, however was always the life of the house.  Company came he'd greet them.  Surgery was on August 20th, Stitches were removed 9/2 and until 9/8 was somewhat normal.  Then we have had major issues.  Hides under furniture and back of closet.  Does not want to move.  Was using the litter box, until the last few days and will not even get up to go.  Will eat, but I have to coax.  Added water to the wet food, thinking he may be dehydrated.  Place him on sofa and will not move.  Been giving him gabapentin in the morning .5ml and .25 ml at night.  Will sleep in the bed all night, usually.  Does not play at all.  Will groom but minimally.  Not sure what to do.  Personality completely has changed.  Looks at things that are not in the room, scared, loud noises startle him (phone, tv) and now the litter box.  He used to be comforted with my husband's shirt, tonight, I laid it by him and he peed on it.  I have turned over the chair that he hides under and limited his access to the bedroom and baby gated the stairs.  Has anyone had any similar issues?  Any advice would be greatly appreciated.  This cat is my world, I am just at a loss.  Thank you all in advance.