Parasitic twin

When a twin embryo begins developing in utero, but the pair does not fully separate and one embryo dominates the other, the weaker twin stops developing and turns into a "parasitic twin" a non-functional, non-conscious collection of extra body parts attached to the healthy remaining twin. Sometimes, the healthy twin is born and raised packing this extra weight. This was the case with Laloo the Hindoo, an Indian man with a parasitic twin attached to his abdomen that had two arms, two legs and a penis but no head; Laloo performed as a sideshow freak in P.T. Barnum's circus at the turn of the 19th century. Today, whenever possible, the parasitic twin is removed. In a recent case in Peru, a three-year-old absorbed his twin into his stomach while the two were gestating in the womb. Doctors successfully removed the boy's parasitic twin Jan. 30. 

Morgellon's disease

There's a new, extremely weird disease in town. Sufferers of "Morgellon's disease," a term coined only one decade ago, feel as if there are things crawling, biting and stinging them below the surface of their skin. Their constant urge to scratch results in insomnia and terrible skin lesions. In January, researchers at the Center for Disease Control and Prevention issued the results of a multi-year investigation of the unexplained condition; they found that patients had no actual disease organisms under their skin, and suggested their sensations were manifestations of "delusional infestation" a false feeling of being infected by parasites.

Maggot infestation

Of all the freaky medical conditions out there, one is most disgusting. A team of researchers at the Hygiene Center at the London School of Hygiene & and Tropical Medicine conducted a survey in 2010 to discover what medical conditions humans are most disgusted by. They presented 20 images of things perceived as repulsive from festering wounds to discolored bodily fluids to more than 80,000 individuals from around the world, and had them rate the images from least to most disgusting. 

The image universally ranked as most disgusting is what you see above the mouth of a man who suffers from a Sarcophagid fly larvae infestation. 

This medical condition ranks as most repulsive, said lead researcher Valerie Curtis, because "disgust is designed by evolution to keep us away from parasites that may make us sick, so people pick up on, and are most disgusted by, visual representations of a parasite invasion."  

Mass hysteria

Other names include collective hysteria, group hysteria, or collective obsessional behavior, in sociology and psychology refers to collective delusions of threats to society that spread rapidly through rumors and fear. In medicine more than one person uses the term to describe the spontaneous manifestation of the same or similar hysterical physical symptoms.

A common manifestation of mass hysteria occurs when a group of people believes they are suffering from a similar disease or ailment, sometimes referred to as mass psychogenic illness or epidemic hysteria.

As the name implies, this little-understood psychological condition sets in among a group of people typically a gaggle of young girls who spontaneously manifest the same or similar hysterical symptoms, such as seizures, convulsions or fainting. Sufferers believe they all have the same disease or illness, but in fact they're all in good physical health. A famous historical case resulted in the Salem Witch Trials of 1692. Dozens of people were accused of (and hanged for) causing several young girls in and around Salem, Mass., to have frequent seizures and convulsions. (The image shows Mary Walcott, 17, convulsing on the courthouse floor during one of the trials.) The girls were posthumously diagnosed with mass hysteria. Accusations of witchcraft no longer fly, but mass hysteria is alive and well. Recently, Thera Sanchez, a high school cheerleader in upstate New York, developed strange physical and vocal tics; this led to a dozen other girls and one boy in her school developing the same Tourette's-like symptoms. Officials initially wondered if the students were being poisoned, but psychiatrists recognized the phenomenon as a modern day case of mass hysteria. 

Mass hysteria manifesting as collective symptoms of disease is sometimes referred to as mass psychogenic illness or epidemic hysteria. Mass hysteria typically begins when an individual becomes ill or hysterical during a period of stress. After this initial individual shows symptoms, others begin to manifest similar symptoms, typically nausea, muscle weakness, fits or headache.