Slowing down, lazy, should I worry?

I know lots of questions about my kittens tonight.

Luna is now 9 months old, Midnight is now 6 months old, and recently, like just these past couple of days, they have both become very lazy. Luna slowed right down after she was spayed. She does play with Midnight, but she can't keep up with him. Now Midnight is full of energy normally he's running around trying to play every minute. The only time he stopped was when he had surgery on his paw. After that he went right back to nonstop play. But the past couple of days all he's doing is just sleeping! He will play games, but normally when I stop, he's still trying to play. Now he walks away on his own, and goes and lays down. The 2 of them are doing nothing but sleeping.

I know their older kittens now. But Lynxx didn't slow down until he was a year old. Their acting like him, at 9 months and 6 months old.

They are both eating fine. Luna isn't a big eater to begin with, but nothing is wrong with her according to her vet. Midnight's eating the same no problems there. Just they are extremely lazy. They aren't sick, no sneezing, nothing like that. Midnight's paw is fine, he was running around and playing. He isn't limping.

So is this new laziness just because they are older kittens now? Or is this something that I should worry about?

I can't get them to the vet until next week when these storms end. We had a good size storm yesterday, a very good size storm today, and 1 hitting here this saturday, the roads are bad enough here, that everything is closed down tomorrow as well.

Ok, thank you guys. I know I over worry about both of them, can't help it.