Another senior cat question

The other day, my senior (15+) Joji would not wake up while she napped. She is a bit deaf so she will not respond to calls. I tap the ground to tell her I am around. I tried that and when she did not move, I petted her. Still she slept. I watched her as she slept, taking note of her breathing. She did wake up after a while. Is this normal?

It happens frequently. I'm a pet sitter and so many of my senior kitties have given me mini-heart attacks just because they were sound asleep. I'd just keep an eye on her and see if there are any other possible signs of illness, just to be safe.

My Cinnie does that some times, she's 10 1/2 but when she was around 4 years old, she went into such a deep sleep, I called her and called her, nothing, then I started to nodge her awake and nothing, she scared me so much I yelled "Cinnie", she jumped up looked around startled like, what is your problem. She was fine. I was a nervous wreck, but she was fine.

My 15 year old sleeps so soundly (on the back of my deskchair) that she falls onto my back several times a day.
I'm paranoid about her hurting herself so I have pillows everywhere beneath her prefered sleeping spots.

Thank you! It's a relief to hear that it is not unusual.