It's disappointing that Netflix doesn't have a more robust horror anime selection, but let's take a look at what they have anyway. Here are all the horror anime currently streaming on Netflix, as voted on by anime fans like you.
Ajin: Demi-Human isn't a strict horror title, but it definitely has some really messed up scenes that will stick with you. Imagine being a human who cannot die, and the government wants to experiment on your body and kill you over and over again in the most excruciating ways possible. Sounds pretty scary, right?
Don't sleep on Ajin, and don't worry about the animation style - you will get used to it. Other horror anime currently streaming on Netflix include the newer series Castlevania, which is exclusive to Netflix, as well as Attack on Titan and Devilman Crybaby.
Vote up the Netflix horror anime you would recommend to other otakus, and vote down anything that you've seen but didn't enjoy.
Attack on Titan (MBS, 2013) is a Japanese fantasy anime television series adapted from the manga of the same name by Hajime Isayama. It is set in a world where humanity lives inside cities surrounded by enormous walls due to the Titans, gigantic humanoid beings who devour humans seemingly without reason. ...more on Wikipedia
Castlevania (Netflix, 2017) is an American adult animated web television series based on the 1989 video game Castlevania III: Dracula's Curse by Konami. The series follows Trevor Belmont (Richard Armitage), who defends the nation of Wallachia from Dracula and his minions. ...more on Wikipedia
Devilman Crybaby (Netflix, 2018) is a Japanese anime series directed by Masaaki Yuasa, based on the manga by Go Nagai. When an ancient race of demons invades the world, Akira Fudo transform into Devilman, possessing the powers of a demon but retaining a human soul. ...more on Wikipedia