A self-described “schizophrenic” threw a brick at his Washington Heights neighbor this week and lunged at her with a knife, yet was back on the street less than 24 hours after cops picked him up.

“I was in shock. I didn’t expect him to be released so quickly, so I hadn’t prepared myself to see him again,” said the woman he targeted, who spoke to The Post on condition of anonymity. “This person threatened to kill me and lives in my building. I want to get him out of the building because I don’t feel safe or comfortable with him living here.”

But beyond the looming threat that the police inaction posed to her lies a more troubling trend, critics say, one that has become prevalent among NYPD rank and file under Mayor Bill de Blasio and his police commissioner of the last two years, James O’Neill.

Last week, cops did virtually nothing about pervy Manhattan apartment doorman Jonathon Aviles, who texted female residents of the building where he worked anonymous photos of his penis and creepy come-ons, despite official complaints from four women in the building.

At least not until The Post reported on the accused stalker and even tracked him down. “There certainly appears to be enough information to investigate further and consider criminal charges,’’ said former Manhattan Assistant District Attorney Mark Bederow.

He’d accessed their telephone numbers from internal building contact logs. By Thursday, cops said they had reopened the doorman case.

And in another instance of police apparently turning a blind eye, a panicked Brooklyn mom who went to her local precinct days ago to report her 9-year-old son and 12-year-old daughter missing was sent away — told by the desk officer to go home and call 911. The officer has since been placed on modified duty.

“They’re not doing their job,” a police source said of the officers involved in all three cases. “These cops are f–king lazy. Ninety-five percent of police officers just get their checks.

“You know the police commissioner doesn’t have your back, and the mayor definitely doesn’t have your back. It’s bad. It’s really bad. It’s bad.’’

The 22-year-old Washington Heights woman, who now lives in fear every time she steps outside her apartment door, said she reported the attack Tuesday, calling the cops on neighbor Roy Rodriguez, 33.

But all they did, she said, was take him to a hospital for a psychiatric evaluation. He was released less than a day later.

Rodriguez told a reporter at his West 174th Street apartment building Sunday that he is “schizophrenic” and hears voices.

“I hear things. I feel things that touch me,’’ he said, using his hand to pantomime something crawling on his arm.

A police source said Rodriguez should have been arrested: “I don’t care if he is [emotionally disturbed] — if’s he throwing a brick and pulling out a knife, he’s got to go to jail.”

Rodriguez admitted having a mental health episode before the incident, saying, “I was coming from Queens on the train. I got scared inside the train, I heard them telling me they were going to harm me.”

He said he got a rock at a park across the street and got the urge to throw it when he saw his victim, who had never seen him before the attack. She described the weapon as a brick.

Rodriguez threw it at her and bolted upstairs, she said.

“He tells me, ‘You know what you did to me,’ and he starts cursing to me in Spanish, telling me, ‘Motherf—er, you know what you did to me,’ ” the woman recalled.

The victim, who lives with kin, immediately told her brother, and the pair tracked down Rodriguez at his family’s apartment.

“His uncle came to the door and told us, ‘Don’t mind him, he has mental health problems, he’s off his medication,’ ” the victim said. “I said, ‘What do you mean, “Don’t mind him”? He threatened me with a brick!’ ”

As the two siblings spoke to the uncle through the doorway, they could see Rodriguez storm into the kitchen, pull out a small knife and start running toward them.

“When he sees me, he snaps again — he’s like, ‘You’re following me, you’re stalking me. I’m gonna kill you,’ ” the victim said.

“’Look what he’s doing!’” the victim said she shouted. “They were able to grab him and keep him from hurting me.”

She called 911, and cops carted Rodriguez off to the hospital for a psych evaluation.

The victim wanted him charged, but cops “told me my charge wouldn’t stick because of his mental health.”

Rodriguez was released from the hospital just after 5 p.m. the next day.

According to hospital discharge papers Rodriguez showed The Post, it was recommended that he undergo “substance use treatment” at a Bronx rehab facility.

The NYPD declined comment. Mayoral spokesman Eric Phillips said, “New York City is the safest big city in America in large part because we have the best police officers in the world. While anonymous sources seek to undermine the police, the mayor will continue to stand with our officers shoulder to shoulder.’’

Additional reporting by Tina Moore and Ben Feuerherd