There are certain psychological conditions which are well-known and often used in sci-fi or fantasy, such as psychopathology or claustrophobia. Psychopaths tend to make excellent leaders (and/or criminals), after all.
However, there are a number of altogether rarer psychological conditions. I was staggered to read about some of them, so hopefully you’ll find this post quite interesting. For those after more information, I strongly recommend Biological Psychology: A Concise Introduction, by Andrew Wickens and Biological Psychology: An Introduction to Behavioral* and Cognitive Neuroscience by Rosenzweig et al.
*Apologies for the American spelling, but despite that it’s a fantastically interesting and rather hefty book.
Lots of people wear glasses, usually because they’re long- or short-sighted (I’m short-sighted). There are a few other problems that can diminish sight, but these tend to be confined to a flaw with the eye itself. Blindsight is quite different. Someone with blindsight has the physical ability to see, but the brain is, for some reason, unable to make sense of the visual information.
In short, a blindsight sufferer can see but does not believe they can. However, there’s a twist. If you were a rotter and threw a ball at them from their blind side they’d reflexively duck or catch the ball. This is because a reflex action is involved. There’s no real cognitive process (if you see a ball heading towards you, you don’t stop and have a think about what to do, it just happens). Even more bizarrely, people with blindsight may be able to point at things that they cannot see, when asked to. They have vision but without the awareness of possessing it. [This is mentioned by Wickens.]
An even more extreme and thankfully very rare condition is fatal familial insomnia. Everybody sleeps. There can be huge variety between sleeping patterns, longevity and how we fare when we skip a night or two, but sleep is literally essential. Fatal familial insomnia strikes the unfortunate sufferer when they’re well into adulthood. It’s a bit of a Ronseal disease: it does exactly what it says on the tin.
Anybody who has gone without sleep for, say, 24 hours knows that it has a pretty serious impact and can affect your behaviour. Prolonged lack of sleep goes far beyond that. After a certain length of time (7-24 months from onset) sufferers die. [This is mentioned by Rosenzweig et al.]
There’s also an interesting distinction between the genders. Women are more susceptible to both stress and depression (the two biggest causes of insomnia), whereas men are far likelier than women to be psychopaths. Anorexia is, of course, predominantly a female condition but there are rising numbers of men (particularly homosexual men) who have it.
It’s very good that there’s a lot more openness about psychological disorders and conditions. I do hope, however, that we don’t end up trying to pathologise every personality quirk and eccentricity.