Type of Spiritual Experience
Although there are a number of papers on Pubmed, the description from Wikipedia is fairly good.
What has been classified as a disease or syndrome is actually often synaesthesia. It was once fairly common amongst shamanic societies, as such one suspects that the cause is the same as it was in shamanic days - drugs or in this case pharmaceuticals.
Unfortunately these days the medical profession treat it as a form of psychotic illness and prescribe yet more pharmaceuticals to 'cure' it, often leading to yet more problems.
A description of the experience
Delusional parasitosis, also known as Ekbom's syndrome,[is a form of psychosis whose victims acquire a strong delusional belief that they are infested with parasites, whereas in reality no such parasites are present. Very often the imaginary parasites are reported as being "bugs" or insects crawling on or under the skin; in these cases the experience of the sensation known as formication may provide the basis for this belief.
The alternative name of Ekbom's syndrome derives from Swedish neurologist Karl Axel Ekbom, who published seminal accounts of the disease in 1937 and 1938. This term is also used interchangeably with Wittmaack-Ekbom syndrome, another name for restless legs syndrome (RLS). Although delusional parasitosis and RLS were both researched by Ekbom, and RLS sufferers sometimes describe some of their symptoms as if they have, for example, "ants in my veins", they are distinctly different disorders. RLS is a physical condition with physical causes, whereas delusional parasitosis is a false belief.
The false belief of delusional parasitosis stands in contrast to actual cases of parasitosis, such as scabies.
People with delusional parasitosis are likely to ask for help not from psychiatrists but from dermatologists, veterinarians, pest control specialists, or entomologists. Because delusional parasitosis is not at all well known to non-specialists, under those circumstances the condition often goes undiagnosed, or may be incorrectly diagnosed.