I sometimes feel slack for not reading non-fiction unless I have to for class, especially for not reading stuff that’s relevant to my majors. Yesterday though, I realised just how much I absorb from the internet, usually via Wikipedia. I started at haunted houses and ended up learning about sleep paralysis, hypnic jerks, infrasound, and the Tetris Effect. All the blockquotes are from Wikipedia.
Sleep paralysis is something many people experience once or twice in their life and some more often. It happens just before you fall asleep or just before you wake up. What happens is you can’t move. Your mind is awake but your body is still asleep. It is also common for people to be able to open their eyes and see, to feel terror, to feel a (usually threatening) presence, to feel pressure on their chest, to hallucinate, or to feel like they’re floating upward. There are other things too but those are some of the most common. Sleep paralysis is a likely candidate for explaining many 'supernatural' experiences, from incubi and succubi to alien abductions.
I get it occasionally and it’s horrible. Often I’m trying to scream or call out to mum but can’t. It seems to happen when I sleep on my back so I try to avoid that. You can read more about sleep paralysis here.
You know how sometimes, when you’re in the process of falling asleep, your body does a random twitch that jolts you awake again? That’s a hypnic jerk. According to Wikipedia there are two theories as to what causes them:
The neurological reason that hypnic jerks occur is not fully understood, although there are two predominant theories.
Some researchers suggest that as a subject's heartbeat and breathing slow down, hypnic jerks occur as a natural part of muscular transition.
Another theory states that as a subject falls asleep, their muscles begin to relax and cease working, causing the brain to believe that the body must be falling through air - and triggering a response to thrash the limbs in an attempt to catch something or turn oneself upright.
Infrasound is sound that has a frequency below 20 Hz. If I remembered more of 7th form physics I would know what that meant. It can be created by lots of stuff, including earthquakes, lightning, and wind turbines. Some animals (elephants, alligators, rhinos, giraffes…) use it to communicate. We can perceive infrasound too, even if we can’t hear it. What I found interesting (and this is the link between infrasound and haunted houses) is that:
Infrasound has been known to cause feelings of awe or fear in humans. Since it is not consciously perceived, it can make people feel vaguely that supernatural events are taking place.
Some film soundtracks make use of infrasound to produce unease or disorientation in the audience. Irréversible is one such movie.
In music, Brian "Lustmord" Williams is known to utilize infrasound to create these same feelings.
Some scientists (Richard Wiseman is one) think it possible that infrasound might explain some of the experiences people have in ‘haunted’ houses. Skepdic has a great article about it.
The Tetris Effect is my favourite. That’s what it’s called when you play a game like Tetris for hours and then keep seeing those stupid blocks whenever you close your eyes.The Tetris effect is the ability of an activity to which people devote sufficient time and attention to begin overshadowing their thoughts, mental images, and dreams.
The Tetris effect can occur with other video games, with any prolonged visual task (such as classifying cells on microscope slides, weeding, picking fruit, flipping burgers, or even playing chess), and in other sensory modalities. For example, there is the tendency for a catchy tune to play out unbidden in one's mind (an "earworm").
Apparently even amnesiacs who can’t remember playing Tetris get it.
I can’t remember where, but I also read that it tends to happen with new activities. I definitely had the Tetris Effect when I started my new job. I’d be trying to sleep and couldn’t get the image of the room I work in out of my head.
Not strictly relevant but funny:

I will be so thrilled if any of this comes up at the pub quiz tonight.
The larger the island of knowledge, the longer the shoreline of wonder. Ralph W. Sockman