Cat acting strange after pill? CRF Civvie

I apologize if this is off-topic but I don't really know where else to turn.

So after yesterday when Sawyer seemed to be doing better (he's our non-diabetic, who was recently diagnosed with CRF and a cancerous tumor) he seems to have taken another downhill turn today. Yoshi says that this morning he was acting average (not high energy, not lethargic) but he didn't seem to be willing to eat. Sort of sniffing at food, licking gravy but not eating. When I got home, I gave him 50 mL of fluids, around 1:40. @ 2:30 he devoured half a can of 9 Lives tender slices chicken. At 4:30 he went to the litter box and had diarrhea, and we noticed him straining. We are unsure if he's peed recently. At 5:30 pm, we gave him 2.5 mg Pepcid. He HATES getting pills, and it was a bit of an ordeal. I gave him a few ml of water with it to wash it down.
Since then, he just seems off. I can visibly see that he's breathing (but seems slow), he sort of just is lying down in various odd positions (like he seems folded in half with his legs splayed out, or sort of like he's having these oddly zen moments. If I pick him up and move him, he walks ok and will jump back on the sofa, but other than opening his eyes sort of halfway when there is a loud noise or if I pet him, he just seems disconnected from the world.

If it weren't for the fact that we have not been able to get more than about 70 Cal. into him today, I'd say I'm just overtired from being up late with Jack last night. But, it just seems like he's shutting down, is the only way I can describe it. Spoke with the vet nurse on the phone, she was not overly concerned except for the possible lack of urine—but the vet that's been seeing him is away for the month. I don't want to take him to the after hours clinic if it's nothing, we're short on cash and the ER is not cheap.

Adding to the difficulty—Sawyer is our third cat. Our first, Ennis, had severe IBD from the day I got him. He was pretty much always in pain and had other difficulties, even when the IBD was under control. Jack has always been fit as a fiddle, except for one bizarre neuro crisis last year (couldn't walk, had a crazy head tilt, never got any conclusive answer for what happened) and now his diabetes. Sawyer has only been with us for a couple of months and I don't have a good sense of what baseline is. He could just be a sleepy kitty, I suppose. But something tells me otherwise. Any feedback would be appreciated.

Since I wrote the above, he's lying downand his legs and head are giving little twitches—maybe like he's dreaming?

Sawyer's Log (food, medicine, etc)

 

Well... the only thing that jumps out at me is that you are giving Mirtazipine a lot. Mirtazipine is supposed to be dosed every 3 days because it has a very slow clearance time from the bloodstream in cats. The smallest pill (for humans) is 15mg and its very hard to quarter them. My vet used a compounding pharmacy and got fast dissolving powder in a capsule. EVen with such a small dose, its recommended for only 2x a week dosing. In cats with kidney or liver disease it should be given even less.

Have you tried cyproheptadine instead?

Oh and my Merlyn got extremely hyper on Mirtazipine, and cypro both, as side effect, but the mirtazipine hyperactivity only lasted one day, not all 3.

 

Is he able to lift his head or is he keeping lower even when walking? Kidney cats can lose potassium quickly due to the increased urination. Low potassium makes a cat very tired, lethargic.

I am always too fast to say check potassium levels, and I apologize for that, but my own little man suffers from low potassium so it's always on my mind.