An early symptom that a disease is developing. Particularly used to describe young people who are withdrawing socially, experienceing developmental disturbances, such as lags in motor and speech/language development, experiencing problems paying attention,impaired memory and reasoning, speech impairments, inappropriate, or flattened, expression of emotion, poor social skills, and depressed mood. Such children may laugh at a sad event, make poor eye contact, and show little body language or facial expression. A bizarre presentation thought to possibly be linked to mental illness.
Also used to describe a woman's presentation immediately before labor starts. Experiencing braxon hicks contractions, dilating, etc.

When you eat dirt for the first time and leave your family to build a shack in the woods

to be experiencing a prodrome

"The prodrome is a phase that comes before an episode of nausea and vomiting in cyclic vomiting syndrome. The prodrome phase, marked by abdominal pain, can last from just a few minutes to several hours. Sometimes taking medicine early in the prodrome phase can stop an episode in progress. However, sometimes there is no warning: A person may simply wake up in the morning and begin vomiting."