I love horror anime/manga, but when I go looking it seems like most of what I find is really action with some supernatural elements. I'm looking for something more psychological, preferably with paranoia or a loosening grip on reality as a theme. Some examples of what I'm talking about:

Paranoia Agent
Serial Experiments Lain
Boogiepop Phantom
Basically everything by Junji Ito
The first story arc in Higurashi No Koro Naku Ni (the rest was ok, but that first storyline where the main character feels like everyone is out to get him and doesn't know why was the best part by far)
Saya no Uta
Another

I've run across a few mentions of a subgenre known as "Denpa," defined as a horror story where the catalyst for the events that occur are based on familiar people acting in unfamiliar, yet seemingly orchestrated ways. Stories where the world seems to have gone mad; and the protagonist is not necessarily an exception. This is EXACTLY what I'm looking for, but I've had a hard time finding much related to it. Apparently it was coined by a few visual novels called "Shizuku" and "Kizuato" but they don't seem to have English translations available. Any recommendations (preferably with a short description or explanation of why you chose it) would be greatly appreciated!

Kikoushi Enma - an OVA series which follows the titular demon with his companions starting a detective agency in the human world in search for other, weaker demons that possess people, driving them out of their sanity. Despite Enma being the star of the show, episodic (mortal) characters get more background than demons do, and the major part of each story is exploration of human terror.

Hm, psychological horror is hard to find. I haven't read or watched any of your examples except Boogiepop Phanthom yet - Lain is on my watchlist - so I can only guess what you're looking for. Have you read Boogiepop wa Warawanai by KADONO Kouhei/ OGATA Kouji yet?

Conductor by KAMINAGA Manabu/ Nokiya might fit although the atmosphere is not nearly as thick as in Boogiepop series. A flutist in a certain orchestra starts having nightmares about a man holding a skull and cannot remember distinct events of her past. At the same time, a strange, headless corpse is found...

Some very light horror can be found in Uroboros no Wa by KANARI Youzaburou/ YAMAMOTO Keiko. It's about some students being forced to curse their classmates in order to escape their own curse.

If it's more about the atmosphere than the genre itself, I highly recommend the "Bungaku Shoujo" series by NOMURA Mizuki/ KOUSAKA Rito, be it "Bungaku Shoujo" to Shi ni Tagari no Douke or its sequel "Bungaku Shoujo" to Ue Kawaku Yuurei. They're both more on the mysterious and psychological side but the setting is fairly dark. Expect there to be lots of twists and tragedies.

In KATOU Haruaki's Abnormal-kei Joshi all characters can be considered bizarre although they live in a perfectly normal environment. It isn't horror but it might be what you'd call "Denpa".

As for anime, only OMORI Takahiro's Jigoku Shoujo comes off the top of my head. It's more tragic than psychologically horrifying, though. Episodes about people who are desperate because of their miserable reality are lined up to a chain of satisfying, yet profoundly sad tales. what connects them is a special service, run by the mysterious "Hell Girl" who will erase a person's existence from your life in exchange for your soul's eternal stay in hell. The manga adaption doesn't compare in style nor in storytelling.

[color=#8A795D]"Stories are what death thinks he puts an end to.
He can't understand that they end in him, but they don't end with him."

• Ursula K. Le Guin, Gifts[/color]

To be savoured:

• Blood Alone by TAKANO Masayuki
• Otoyomegatari by MORI Kaoru
• Gangsta. by Kohske
• Seishun Kouryakuhon by AKIZUKI Sorata

Ghost Stories-I guess, it's mostly comedy.
Blood- C Never saw it though. Too scary!! 😔 I'm a wimp, though.
Umineko no Naku Koro ni- It wasn't really scary for me. That could be because I'm bias to looks.I rather a bishie kill me than a monster. Then, I'll die looking at eye candy. 🤣
Attack on Titan- it's more of a action type like you mentioned.

I feel like there's more, but I can't remember. I'm not really into horror, but hope I helped! 🙂

“The mind is its own place, and in itself can make a heaven of hell, a hell of heaven..”
― John Milton, Paradise Lost

Kikoushi Emma sounds like it has a lot of potential, as does Jigoku Shoujo. I'm very interested in the emphasis on desperation and loss that they both seem to have. Keep 'em coming!