Alien hand syndrome sounds really cool, but it is hard to imagine it being anything but extremely frustrating for the person experiencing it. Basically, it occurs when an arm seems to have a mind of its own; it moves around, grabs hold of things, and responds to to the touch of another person—but it does this without the control of the person to whom it belongs.
As you’d expect, this nightmare syndrome can lead to great distress on the part of the sufferers, who often refer to their rogue arm as though it were a separate entity.
This phenomenon is most widespread in Japan, or more specifically, among those who grew up according to the customs and social expectations of Japanese culture. Taijin Kyofusho is characterized by a crippling fear of social interactions, and a vivid awareness of everything that could possibly go wrong, such as having an offensive body odor or doing something that will offend someone in any other way. That the condition should arise in Japan is in many ways unsurprising, since Japanese culture is well known for placing importance on keeping up appearances and etiquette in social situations.
Erotomania is a pretty strange disorder; essentially, it refers to people who are deluded into thinking that someone else is in love with them. But what makes this disorder especially bizarre is that the person who is supposedly in love with the sufferer is usually someone of much higher status than themselves—and often a celebrity.
This delusion can be difficult to break; even if the supposed lover directly denies any feelings of love, it is often not enough to convince the deluded individual. Unfortunately, there isn’t much known about this particular disorder, especially in regard to its treatment.
Riley-Day Syndrome is also known as Familial Dysautonomia; and it’s a disorder that is genetically inherited. To actually show signs of having the condition, however, the relevant gene has to be passed on by both parents.
Basically, Riley-Day syndrome affects the autonomous nervous system. While there are many extremely unpleasant symptoms (such as frequent vomiting, and difficulty swallowing), it does also have some arguably cool features. Chief among these is the fact that many people with the condition are almost entirely insensitive to pain.
Of course, though a painless life sounds great in theory, it doesn’t work so well in practice. Pain is actually your friend; it sends signals to your brain to let you know when something needs fixing—so to go without it altogether isn’t necessarily going to be a pleasant experience.