Hey KittyCats,
This is not at all an uncommon issue, especially not with cats that you sometimes pick up and snuggle. -Even if they NEVER go hungry, ever.
I also had cats born at the EXACT same time suddenly have opposite sleeping patterns - one was 50% and sleeping, while the other was 50% and awake! -Hence, they obviously never really had a kitten
Luckily I discovered the problem just as they were both at 50%, so solving it was really simple - but I still wonder how on earth it happened.