I have two very elderly cats.....

[BertrandRussell]

....both in excellent health. Maybe slowing up a little, far fewer half eaten dead rodents than there used to be!

One thing I have noticed- they are both finding more and more bizarre places to sleep. Places that have been there and ignored all their lives. One is currently snoozing away in the top of a sack of potatoes, so not particularly warm and cozy for old bones! Yesterday the other spent most of the day stretched out on the piano keyboard. Is this usual? A sign of increasing eccentricity? They have two cat beds, a dog bed and 4 human beds available. Not to mention several sofas and chairs!

I had to google this and it seems while it MIGHT indicate that there is an underlying health issue, it also may not!! So no help at all. Sounds like they have great run of the house :)

I’d move them. I move mine if he sleeps somewhere cold.

The one on the piano was perfectly warm. I daren’t move the one in the potatoes- he’s scary..........

Aw. I think we need pics before we can advise
My old girl was 18 when she passed away, she would sleep curled up next to a pair of shoes, or in the middle of a pile of lego (really!) I tried to get her to sleep in a variety of cosy cat beds but she wasn't having any of it. Bonkers cat but I loved her.

Apparently 50% of cats aged 15 and up actually have dementia, which could explain changes in behaviour.

None of mine are elderly yet - but one currently sleeps on a box of lego in the hall upstairs, one in a tray of car parts in the hall downstairs (that I really should put away..), Basil sleeps in the intray on the kitchen table and only Sybil has the common sense to sleep curled up on a comfy chair. Give it a couple of weeks and they'll all be somewhere different but equally daft.
So I don't think you need worry too much.

In a year, my girl went from being a constant lap cat to spending a lot of time on her own away from us. It might just be the one on potatoes wants a quiet spot.

How old are they? We'd love some photos if you can post.

Well on mn any elderly eccentricities are always dementia!
Yabu to post about your elderlys without pics.

Maybe they are having a cat planking competition, perhaps check their internet history.

Are they lying in their usual fashion? I've been to the vets with my 16 year old cat today, and she has muscle wastage in her back legs (amongst other things), vet thinks she may has arthritis. She does now only lie in a sprawl, whereas she'd normally favour the chicken pose. Vet said it's harder to tell when cats are getting arthritis as they mask it more.