For some reason, there are still a lot of people that put flea products, intended for dogs only, on cats. Maybe they don't see the "no cats" symbol, or they do, and don't believe that something that works just fine on dogs would cause a problem for a cat. It might seem obvious, but they told us this in vet school, more than once: "Cats are not small dogs." On occasion, though, we do see dogs that act this same way (generally not as severe) - they tend to be the small dogs.
Here's what happens when you put Sargeant's on a cat:
These chemicals really play hell with a cat's nervous system, and this constant muscle activity can mess up their metabolism, and increase their body temperature. They need treatment, as soon as possible - a bath in warm water with a detergent shampoo to remove the product, a thorough drying to prevent hypothermia, and support with IV fluids and a special IV muscle relaxant.
That same kitten, after treatment, sleeping peacefully:
