Currently, most authentic Chausies produced are late generation cats with fully domestic temperaments. Their TICA registration certificates will usually indicate that they are "C" generation or "SBT," which nearly always means they are four generations or more beyond the jungle cat (F. chaus). In cases where they are "A" or "B" generation, it is usually because they have been recently outcrossed to another domestic breed to improve specific cosmetic traits, but the cats are nonetheless more than four generations beyond the handful of nondomestic ancestors.
Watching the rate of breathing is one of the simple observations that you can make on a pet cat at home. This cat has a problem known as "tachypnoea", which means rapid breathing. IF you watch her side carefully, you'll notice that her sides are moving much more quickly than a normal cat at rest. Her problem is being investigated, so the precise cause is under review, but it's most likely that she has "hyperthyroidism", caused by a benign tumour on her thyroid gland
Long term prognosis for recovery of your cat will vary from cause to cause. Infections and pneumonia are serious illnesses that need a high degree of specialized veterinary care. In all cases, your cat’s chances for a full recovery will increase if immediate veterinarian care is sought as soon as initial symptoms are detected. Additionally, given the seriousness of lung and breathing issues, you should follow up after symptoms in your cat have resolved in order to prevent potential recurrence.
Queening is a painful process just like childbirth is for humans and some heavy breathing or panting may occur afterwards for a few days due to discomfort. But if you feel that she is straining or in distress you should visit your Veterinarian to check her over to ensure that there isn’t a retained kitten or another issue leading to these symptoms. Regards Dr Callum Turner DVM
Lethargy and increased respiratory rate are not specific symptoms as they are shared with many conditions; however I’m concerned that they are a common sign that an animal is in pain, but without examining Marilyn I cannot say whether she is in pain or there is another cause for the symptoms. You should visit your Veterinarian for an examination to be on the safe side especially if this has been going on for a day or more. Regards Dr Callum Turner DVM