Eating again but sill not himself. Not sure what's wrong

Max has been really unwell and barely eating since 18th june. At some points he wasn't eating at all. Found out he had CKD on Monday and is going blind in his left eye. Its been really critical at times and heart breaking. He was completely motionless all day for 3 days except to drink or pee. His ears didnt react to noise at all. Didn't open his eyes most of the day.

Now he's on cerenia and eating again. Not as much as he should but enough to sustain him and its getting better each day.

Hes drinking and peeing and has finally started pooping after days without, most likely due to lack of food to produce a movement.

He seems more alert and is interested in his environment again.

Unfortunately hes not grooming, very hissy and defensive now toward me, unless I have food hes highly suspicious of me. Can't get him to take the gabapentin, smells weird so he wont eat food with it in. And hes really aggressive now if I approach with a syringe.

Doesn't leave the one room hes been in since we got back from the vet Monday. Stays on the ground at all times, not using furniture or his cat tree.

He's clearly uncomfortable or unsettled but I dont know what it is. Im new to this. And he's only 8 for context, not very old. CKD is only stage 1 or 2, no protein creatin in his urine sample, liver and thyroid were excellent.