What is it?
Munchausen syndrome is a psychiatric condition, in which the person exaggerates or creates symptoms of illness or psychological trauma in order to gain attention, sympathy, or reassurance. In some cases the affected can know a whole lot about medicine and pretend to have highly specific symptoms, which can lead to very costly and lengthy medical analysis and unnecessary operations. It should be noted that people who suffer from Munchausen syndrome do not, unlike in other disorders, do what they do for financial gain, and neither is the whole process unintentional or a product of their imagination.
The prevalence of Munchausen syndrome is very hard to find out. It has been estimated, however, that about 0.2-1% of hospital inpatients in the US would be affected by something like it.
What causes it?
Things that increase the likelihood of developing Munchausen syndrome include childhood trauma, growing up with emotionally unavailable parents, being seriously ill while a child, having tried and failed to get a career in a medicine-related field, and personality disorders.
What happens during it?
The mechanisms of Munchausen syndrome are unclear. The patients may try to act again some unresolved problems with their parents. They may have been sick before and become accustomed to the role of a sick person, and so they might try to get back to that “safety”. They may have seen someone close to them be sick and become envious of all the attention they had received.
How can it be treated?
If a person with Munchausen syndrome has another underlying mental condition such as a personality disorder, that should be addressed as a priority. Other than that, the treatment of people with the syndrome can be very tricky. It is common for them to for example try to split up the team of professionals that treats them, which is in part why some people recommend not treating Munchausen syndrome sufferers at all unless they show a genuine willingness to get better. Sometimes the syndrome can get so severe that the patients are a serious risk to their own health, and on these occasions it might be necessary to hospitalize them.
Sources: https://en.wikipedia.org/wiki/Munchausen_syndrome, https://en.wikipedia.org/wiki/Factitious_disorder, http://emedicine.medscape.com/article/291304-overview#a1