u/Balquis1

Our female Maine Coon is 7 years old and weighs 8kg (we put her on a diet recently so hopefully her weight will lower a bit) She is usually very cuddly but recently she started behaving weird.
On Wednesday evening she seemed quite lethargic and barely reacted to anything so we went to the vet the next day, who told me she couldn‘t see anything wrong.
We did an Xray and the vet told me her spine might be causing her some pain. They gave me Metacam for her pain and the moment we got home she seemed to do better. She was moving more and purring when we pet her.
We still gave her the Metacam and on Sunday she seemed to get worse again. Went to the vet again on Monday who tested her blood but didn‘t find anything. They told us she has Arthritis and to keep giving her Metacam till Thursday.
However now she seems to be getting even worse. Yesterday I gave her Metacam and she just slept the whole day and has been eating less. Today in the morning, I found her sleeping in the basement in a laundry basket which is unusual for her.
I brought her upstairs and when I set her down she had a lot of trouble walking, with her back legs slipping from under her. Now she is back to lying down in a corner, sleeping and I don‘t know what to do. Is it really possible for Arthritis to make a cat behave so differently from one day to the other? Why does my cat seem to deteriorate so quickly? I just think that Arthritis might not be the only issue and I am scared that she will get even worse.