Jörg Buttgereit said in an interview that he never intended to be a director and Nekromantik was just a film to rebel against the German film rating system, trying to shock as many people as possible.
The main corpse's eyes were actually pig eyes that Jörg Buttgereit had acquired from a slaughterhouse by claiming to be a medical student.
(at around 50 mins) When the protagonist, Robert, is watching a fictional slasher film in the movie theater, the screaming sound effects towards the end of the scene are directly taken from the infamous "Splinter Scene" of Lucio Fulci's film Woodoo - Die Schreckensinsel der Zombies (1979).
Website Horror.Land listed this as one of their "Horror Films We Only Watch for the Nudity" in 2020.
In the bedroom, there's a picture of Charles Manson. He was a notorious cult leader who was convicted of first degree murder and the conspiracy to commit murder.