URGENT - Please Help

This is our happy lovely little friend Ferocious Beast. She was always been our happiest, most energetic, friendliest baby. She has been slowing down the past few days and today has been puffed up, and closing her eyes a lot. She continued to run around and play a little so i left her alone. I looked out about an hour later and she had stopped, and wouldnt move. i could see she was twitching/gagging from the house. we went out and put her in the cozy cat carrier. she’s inside the house now resting. she started to fall asleep but then stood up and started to do this. there is obviously something wrong and we want to help but don’t want to make it worse. has anyone seen this before?