Why Does My Kitten Run Around Like Crazy Growling At Everything?

my kitten runs around like crazy growling at everything and doesnt go into her litter box. she is only about 6 months old. what could be wrong?

why does my cat run around like a nut? his tail is wagging but the rest of him looks sad and depressed. he wont sleep or eat, just keeps running back and forth in circles. whats going on???