Cubby use to do that as a kitten but after he played for an hour he would sleep the rest of the day. When I took him into the vet they told me he had heart problems and that they were slowly going away. And now he will still play to the point where he has to lay down for a few minutes or I will mist him with water if he is getting to hot or panting to much for my liking. Another thing I do to him (well for him) I will fill a frozen mug up with water and let it set for a few minutes and take it over to him and set it down right in front of him and let him lick the sweat from the mug off and that cools him down alot. His heart problems have healed now. So all the playing he has missed while he was a kitten is coming out now. But as long as he is happy and healty I don't mind. Just keep an eye on her and make sure she doesn't get to bad.