This characteristic typically manifests as an indifference to other people. In contrast to introversion, a nonpathological dimension of human personality, social anhedonia represents a deficit in the ability to experience pleasure. Additionally, social anhedonia differs from social anxiety in that social anhedonia is predominantly typified by diminished positive affect, while social anxiety is distinguished by both decreased positive affect and exaggerated negative affect.This trait is currently seen as a central characteristic, as well as a predictor, of schizophrenia spectrum disorders. Signs and symptoms
Decreased ability to experience interpersonal pleasure
Social withdrawal/isolation
Decreased capacity for social contact and interaction
Lack of close friends and intimate relationships, and decreased quality of those relationships
Poor social adjustment
Decreased positive affect
Flat affect
Depressed mood
State-related anxiety

Background and early clinical observation
The term anhedonia is derived from the Greek an-, "without" and hēdonē, "pleasure". Interest in the nature of pleasure and its absence dates back to ancient Greek philosophers such as Epicurus. The symptoms of anhedonia were introduced to the realm of psychopathology in 1809 by John Haslam, who characterized a patient with schizophrenia as indifferent to "those objects and pursuits which formerly proved sources of delight and instruction". The concept was formally coined by Théodule-Armand Ribot and later used by psychiatrists Paul Eugen Bleuler and Emil Kraepelin to describe a core symptom of schizophrenia. In particular, Rado postulated that schizotypes, or individuals with the schizophrenic phenotype, have two key genetic deficits, one related to the ability to feel pleasure (anhedonia) and one related to proprioception.
Hyperemesis gravidarum (HG) is a pregnancy complication that is characterized by severe nausea, vomiting, weight loss, and possibly dehydration. Feeling faint may also occur. It is considered more severe than morning sickness. Symptoms often get better after the 20th week of pregnancy but may last the entire pregnancy duration.The exact causes of hyperemesis gravidarum are unknown. Risk factors include the first pregnancy, multiple pregnancy, obesity, prior or family history of HG, trophoblastic disorder, and a history of eating disorders. Diagnosis is usually made based on the observed signs and symptoms. HG has been technically defined as more than three episodes of vomiting per day such that weight loss of 5% or three kilograms has occurred and ketones are present in the urine. Other potential causes of the symptoms should be excluded, including urinary tract infection and an overactive thyroid.Treatment includes drinking fluids and a bland diet. Recommendations may include electrolyte-replacement drinks, thiamine, and a higher protein diet. Some people require intravenous fluids. With respect to medications, pyridoxine or metoclopramide are preferred. Prochlorperazine, dimenhydrinate, ondansetron (sold under the brand-name Zofran) or corticosteroids may be used if these are not effective. Hospitalization may be required due to the severe symptoms associated. Psychotherapy may improve outcomes. Evidence for acupressure is poor.While vomiting in pregnancy has been described as early as 2,000 BC, the first clear medical description of HG was in 1852 by Paul Antoine Dubois. HG is estimated to affect 0.3–2.0% of pregnant women, although some sources say the figure can be as high as 3%.