I lost two cats in three weeks maybe ten or so years ago. The first one died of old age; she woke that morning and had trouble standing/walking. We made her comfortable and called the vet who couldn’t see her right away. My ex sat with her while I kept my son distracted, and she passed away mid morning peacefully. She was about 19.
The second was only five years old. My ex noticed she was sluggish and not eating, and took her to the vet, who found that her kidneys had shut down. Apparently as a kitten, raised in a garage, she’d drank antifreeze and it finally caught up. This was my 10yo son’s cat. We all went to the vet and said goodbye and it was quite hard for everyone.
We went straight to the shelter after and got two more cats, two lovely sisters who are still with us.
Sorry for your loss.