Still concerned about Oliver

I posted in here maybe a week ago, concerned about my 9 1/2 year old rabbit, Oliver. He's been to his rabbit-savvy vet twice and she can't find anything wrong with him, but he's still acting weird. I'm wondering if anyone has any ideas about what could be going on, because his vet and I are at a loss and I really want him to be better.
Although he is still friendly, grooming, pooping and purring,
I am still concerned because has gone from running around the house to remaining mostly stationary in a matter of a few days.

Here's the symptoms:
decreased appetite, yet still eating, just slower and less enthusiastically
head jerks (described online as rabbit hiccups) about twice a week
hind leg cramps (I have witnessed it twice)
heavier breathing but not labored along with snoring while sleeping
sudden change in behavior--no longer interested in his dog companion, little interest in hopping around, mostly laying around and napping


Here's what its not (according to the vet/per test results):
Pneumonia
Molar spurs
E. Cuniculi
GI Stasis
Renal Failure? (his BUN is 27 and his creatinine is at a normal level, my vet doesn't think this is of concern)

He has minor arthritis, which he takes metacam for and minor cataracts.

I'm at a total loss, and all he does is lay around. Did his age just catch up to him suddenly? If so, does this mean he's reaching the end?
He also eats kale on a regular basis--could it be oxalate toxicity?

I know this is a long post, and the likelihood of any ideas is slim, but this is my last hope of figuring out whats going on.

Thanks in advance.

Has your vet ruled out heart issues or possibly a thymoma? I have read of frequent hiccup episodes sometimes accompanying these problems. I can't recall, but have xrays been done yet(or not because you don't want to risk a GA?) to rule out cancer?

Old age is certainly possible as well. My 9 year old bun certainly sleeps a lot more now, has slowed down quite a bit, and is harder to keep her weight up. But this has all been more gradual with her. With this being a sudden change for your bun, I would think it more likely a health issue. Though it doesn't sound like it is causing him pain and discomfort, just fatigue and reduced appetite.

Yep that's right. And yes, I have had x-rays done for him since I last posted. The vet said everything looked good. The vet agrees that something is wrong but doesn't know what else to do to figure it out.
Would an x-ray have showed a thymoma or heart problems? If not, what could we do to find either?

How much is more sleeping for your 9 year old bun? Because mine just sleeps until about 6pm then hops around and chins things for about 5 or 10 minutes, sleeps, grooms himself for a few minutes, lays around, eats some hay, lays down, eats some grass and it continues like that until I put him in his cage to go to sleep.
I don't want to over-test him and make him unhappy, and I'd really really really like this just to be a happy and aging bunny.
Could this be his new normal?

An xray can show some heart problems or thymoma, but some vets may miss seeing it. If your vet isn't a specialist, maybe your vet could consult with a specialist and have them take a look at the chest xray to see if something was missed.

With something like thymoma, at your buns age it would probably be more about providing supportive care and making him as comfortable as possible. But with heart issues, it may be treatable with medication to get him more back to normal.

Here's some info on xrays and thymoma, and heart problems. These are just possibilities though, based on some similar symptoms of rabbits with these issues. It may be something else entirely. And if your vet is a really good rabbit vet, these things may have been ruled out already.

http://www.medirabbit.com/EN/Cancer/Thym/Thymoma_rab.htm (this is just to show you the xray checking for thymoma)
http://www.medirabbit.com/EN/Cardiology/Cardio/Cardio_en.htm (GRAPHIC MEDICAL RELATED PHOTOS)
http://www.medirabbit.com/EN/Cardiology/Failure/congestive.htm