There are several reasons why cats run wildly back and forth:

1. This is the natural instinct of catching prey. Many cats will still retain some of their instincts after being raised at home. When I see some moving things or small insects at home, I can't help but chase them.

2. The cat may be dirty, which will make the cat feel uncomfortable. The uncomfortable feeling will cause the cat to run back and forth.

3. It is to consume the cat’s excess energy. When the cat wakes up and has nowhere to vent its energy, the cat will spend its time running back and forth.

How to deal with fleas on cats:

1. Clean the cat regularly and promptly, mainly bathing and combing the cat's hair frequently.

2. You must maintain household hygiene at home, keep windows closed, and reduce cats from going out.

3. Disinfect the places where cats like to stay, especially litter boxes, toys, etc.

4. Regularly deworm the cat externally, and use drugs to drive away fleas on the cat’s body.

5. Take your cat to bask in the sun when you have time. Sunlight can not only drive away fleas, but also supplement calcium.