To harrow is to cause worry and upset, the way a truly scary movie might harrow you, making it hard to sleep without turning on the light.
Harrow is an uncommon verb that was originally used in a religious context. You're much more likely to hear the adjective harrowing used for things that are extremely distressing. But if your cat torments you nightly with her incessant meowing, you might try yelling, "Why do you harrow me?" In agriculture, harrow has a completely different meaning: it's a device that helps up break up the soil. And if you harrow your land, you use such a device.