I have to say that the question is poorly formulated. There is an element of truth about it but it’s formulation misleads. The question should be, “Is it true that cats find a place to hide when they are badly injured or very ill?”
The answer to this question is of course, yes. When cats are injured they are in a vulnerable position. Like all animals cats, including domestic cats, are good survivors and they find ways to survive. If they are injured or sick they will find a quiet place to hide which protects them from predators. They would hope to recover. I’m not saying that they consciously wait to recover. They just know instinctively that they are unable to defend themselves or hunt. Their instincts kick in and they pause in a safe place.
The question that is asked also begs a second question which is whether cats know that they are dying. After all, if they do not realise that they are dying the question in the title is meaningless. I don’t believe that cats know that they are dying. It requires an element of self-awareness to realise it. In my view domestic cats are not self-aware although this is a contentious point. People are not sure whether they are self-conscious or not.
To recap, I would argue that cats do not know that they dying and they do not hide when the dying because….they don’t know they are dying and are not self-aware. But they do know they are injured and unable to perform normally. There are also instinctively aware that the need to protect themselves by hiding. That I believe is the full answer.
I have a tragic personal story which illustrates this topic. In 1994 I lost my darling female cat. She was injured on the road outside my house. It was my fault that she was allowed to go out and I deeply regret it. I searched for her when I came back from work. I knew that something bad had happened. I found her under a bush on the other side of the road where she had been hit by a car. She must have run from the road to this bush. She lay down there, hiding until she passed away. If you’ve lost your cat and you think that she may have been killed on the road, look under a bush near the road and you might be lucky. However you will be very sad as I was for many years afterwards. I still am. I still feel the guilt of it. If there is a rainbow bridge I hope to pass over it to meet her again on my passing. That would make me incredibly happy.
Illness and pain
We know, too, that when domestic cats are unwell, anxious or feeling distressed and in pain, they tend to find a quiet spot to hide or rest and recuperate. The spot may be under a piece of furniture so that they are protected from above as well as on the sides. It is certainly sensible to provide a hiding place where your cat can take advantage of such a place. Cats need them not only to recuperate but to rest safely. Perhaps it is the sensation of pain which triggers a cat to find a safe place to hide.
Postscript: I can’t show a picture of a dying cat under a bush because that would be deemed unacceptable by my advertisers upon which I rely for a very, very modest income to help run this website! So you have a predator of cats instead.