Valetudinarian refers to a sickly or weak person, especially one who is constantly and morbidly concerned with his or her health. It is likewise, a descriptive word which means chronically ailing; sickly and constantly and morbidly concerned with one's health.
"Valetudinarian" is not a term commonly used in the field of psychology. It refers to a person who is overly concerned with their health and constantly worries about being ill. This term is more commonly used in general medicine or related fields.