2. The reason why cats purr is the sound made through the throat cavity when the false vocal cords vibrate. This phenomenon mostly happens when cats are satisfied, excited and relaxed.
Just because a cat purrs doesn't mean it's asleep, on the contrary, it's probably not asleep at this time. Because cats don't purr when they are playing, nervous or sleeping.
4. Some people think that the purring of cats is beneficial to stimulate muscles and bones, and a certain frequency of vibration is beneficial to keep bones and muscles in good condition.
Some people think that the purring of a cat really releases its own pressure, and it can be heard when it is injured, broken or painful. Of course, some people think it is a cat respiratory infection.
It's okay. Don't be afraid. It's normal.