Old Cat's Behavior Change

My cat is ~11yrs old, and her behavior has changed recently. She's eating more slowly/a little less, not quite as eager to play, and she's started sleeping in her carrier instead of on my bed sometimes. My bed is about waist height, but she's got a perch so she can take it in two steps and she's capable of jumping all the way up, though she doesn't do it often. She still sleeps on my bed when I'm not in the room but she used to sleep exclusively on my bed. She's also a bit less vocal and cuddly and is playing less.
Things that have changed: her first flea&stick treatment in ~6 months (she's an indoor cat and there are no other pets) and I changed my sheets.
I'm not sure if she's sick, aging, or simply dislikes the heat (my room is usually ~72 degrees Fahrenheit bc my air conditioner isn't very good). She isn't dehydrated, throwing up, drinking less, avoiding the litterbox, ect. She just seems a little down.

Thoughts?

When was her last vet visit?  A check up and blood work to rule out any medical issues may be a good first step.

Do you have any lucky bamboo plants or lilies?those can be [emoji]128128[/emoji]For a [emoji]128049[/emoji]

Cats do do funny stuff, often for no discernable reason.

My cat began sleeping on my bedroom floor at around 13 years old after years of sleeping on my bed.

He did come back every once in a while for the night (and he would always spend time with me there watching dvds etc of an evening) but as soon as the light went out, he was back to the floor. I have no idea why.

If she's eating slower and seems a little down, it might be worth checking out her teeth and gums?

Eddie looked very down in the mouth (literally!) when he had teeth problems. He had 4 extractions and once he'd recovered he was a different cat.

@lunatuna How's your girl doing now? Did you get her checked out?

E edwardthefirst she has actually gotten quite a few teeth extracted. She's missing ten teeth, some of which I assume fell out (I don't have very much history on her). But I clean & check her teeth regularly.

Columbine I've actually figured it out. I usually have curtains surrounding my bed, but I didn't have them up this summer because I was in a temporary housing situation. She's just a little cave cat! She's back to sleeping on my bed almost exclusively now that it's covered and she's back to being as cuddly and playful as ever (and maybe even more vocal).
I think she wasn't playing and eating like normal because of the heat. I'm now in a room with much better air conditioning and she's doing excellently. She just likes to sleep where there are as few open sides as possible, and she was probably too hot to share body heat through cuddling.

(Unrelated, I'm sorry I didn't answer earlier. I didn't get email updates)

good job figuring it out.  i'm glad to hear your cat is happy again and everything's back to normal