When cute becomes scary

This is going to sound strange, but Penny is acting differently.

If you understand what I mean, it's that issue where you've had a cat for several years, and then there's a sudden change in behavior, which, as I understands it, indicates something may be wrong.

Yesterday morning, I found Penny laying in my wife's recliner. I thought nothing of it, even though she never lays there.
Later yesterday, she started doing something we thought was really cute. She was standing in the chair, chasing her tail.

She's been doing exactly that for a full day now, whatever chance she gets. Wearing herself out to the point of exhaustion. Falling off the chair dizzy.

We haven't seen indication of her doing this anywhere else, such as in their room at night, but she wasted no time this morning coming down and jumping into the chair to continue this oddity.

I've seen animals chase their tails before, but doing it for hours on end has me worried.

Does anyone have any advice on this? Experience?

Mine will jump suddenly and bite their tails furiously if fleas are a problem. My first Coonie started gnawing her tail and then the tail looked bent, so we took her to the vet thinking it was a broken tail and it turned out to be a huge abscess that needed lanced and stitched!!
My Mandy likes to chase her tail when she's feeling frisky and also when she is bored and I'm too busy to lavish attention on her. But she's never done it for more than a few minutes. My first instinct would be fleas or an allergen that is making your cat uncomfortable, maybe do a good workover with a flea comb and see if you catch any, and try to inspect her tail for anything else unusual. Coonie tails are dense forests all on their own-anything might be in there!!