A normal explanation for some hauntings

https://www.higgypop.com/news/carbon-monoxide-tricks-you-into-thinking-your-home-is-haunted/  Selected Quotes:

You may have heard the theory that a carbon monoxide leak in the home can lead people to have paranormal-like experiences including nausea and even hallucinations, but is there any truth to this claim? . . .

More extreme exposure can result in chest or abdominal pain, delirium, and audio and visual hallucinations. This is why some people living in haunted homes might report seeing or hearing ghostly phenomenon. However it should be pointed out that carbon monoxide induced hallucinations only happen in cases with high level or longterm exposure to the gas. In these extreme cases the sufferer is also risking seizure, fainting, coma and death. So by the time someone reports visual disturbances it should be clear that something much more serious is going on than just having a resident spook.

It's easy to see why a source of carbon monoxide in a home could make you think the house is haunted. After all, the gas is likely to affect everyone in the property, so you'll all have similar experiences, and the uneasy feelings and symptoms will pass once you leave your home, as it would with a ghost focussed on your home.

Arguably a carbon monoxide induced haunting might be more common in a an older property. Although there's no figures to back this up, it seems logical that an older property might have out-of-date appliances which aren't in a good working order. This could at least start to explain why old and creepy houses often have a haunted reputation.

The link between carbon monoxide poisoning and haunting experiences is nothing new, it was first written about by American ophthalmologist Dr. William H. Wilmer in 1921 ... Wilmer shares an account written by a woman who he called "Mrs. H". The mother describes her experience with carbon monoxide poisoning and how her household mistook it for a violent haunting.

The family spent the winter of 1912 living in a large house that was built in about 1870 and was in need of repair. The house had no electricity and was lit by gas lights throughout, with an old furnace that broke down on their second day in the house ... Mrs. H claimed that after just a few days in the house her and her husband started feeling "very depressed", this escalated to severe headaches and feeling weak and tired. She later reported aches, pains and unusual dreams.

In just a few weeks the family reported hearing footsteps in parts of the house but upon investigation found those areas empty. Their houseplants died, and they felt as if they were being watched to the point they moved furniture around so they could keep an eye on the spaces behind them. They were awoken at night several times by the sound of a bell or the telephone ringing, as well as by slamming doors and loud footsteps. The mother reported that her children grew pale and suffered from heavy colds, became lethargic and lost their appetite. On top of this they also experienced strange goings on, including hearing phantom voices. One child also reported being attacked as he slept. He suddenly awoke and ran though the house screaming "Don't let that big fat man touch me." ... Perhaps the most disturbing phenomenon was the sighting of apparitions. Mrs. H reported seeing a strange dark-haired woman in a black dress in the dining room, but as she approached the figure disappeared. She wrote, "In her place I saw a reflection of myself in the mirror, dressed in a light silk waist."

It wasn't just the family that was experiencing these odd happenings, their servants were too. The children's nurse had been the first to declare, "This house is haunted" after hearing footsteps herself, feeling like she was being followed, and even awoke to see a mysterious man and a woman sat at the foot of her bed.

The story is so convincing with so many witnesses that it would be easy to be sucked in by the claims of a paranormal explanation, but Mrs. H was not convinced by this and called a professional for help. It was later discovered that the furnace was in a very bad condition and had been spewing carbon monoxide fumes out into the house instead of going up the chimney. A physician examined the family, he told them to take iron supplements and not to spend another night in the house.

Carrie Poppy, a paranormal investigator and podcast host described a similar paranormal experience fuelled by a carbon monoxide leak in her 2016 TEDx Talk in Vienna ... Carrie said, "One night, I was sitting there and I got this really spooky feeling, kind of the feeling like you're being watched. But no one was there except my two dogs, and they were just chewing their feet." She continued, "The feeling just kept getting worse, and I started to feel this pressure in my chest, sort of like the feeling when you get bad news." Over the course of a week the feeling got worse ... and Carrie ... started to hear strange sounds like whispers ... Carrie said, "I looked it up, and the symptoms of carbon monoxide poisoning include a pressure on your chest, auditory hallucinations and an unexplained feeling of dread."