Young children who are otherwise completely normal suddenly begin experiencing severe nausea and vomiting, with the symptoms lasting for several days. Doctors who treat these children diagnose them with Cyclic Vomiting Syndrome. The condition is treatable.
Description of Cyclic Vomiting Syndrome
Cyclic Vomiting Syndrome causes stomach pain as well as severe nausea and vomiting that lasts for several days during an attack. This condition has no known cause, according to the Mayo Clinic. While this syndrome of constant vomiting in children does begin in childhood, it potentially can begin at any age. As a child with this condition reaches her teen years, she can outgrow the illness. If it lasts into her adult years, she may experience fewer episodes of CVS, but each episode may last longer than they did in her childhood years. 
Primary and Secondary Symptoms
Primary symptoms of CVS include loss of appetite, nausea, a pale complexion that develops before an episode of vomiting, severe vomiting, gagging and extreme tiredness. These symptoms can appear, on average, six times an hour. A child with this syndrome may experience up to 10 episodes a year, with each lasting one to two days at a time; adults have about four episodes annually, but each one lasts nearly a week. When an episode begins, it is usually late at night or early in the morning, states the Mayo Clinic.
Those with CVS may go on to develop fever, headache, dizziness, diarrhea, sensitivity to light and abdominal pain. 
Some causes of CVS include motion sickness, emotional excitement or stress, colds, sinus problems or allergies, menstruation, consumption of chocolate or cheese, physical exhaustion, overeating or eating immediately before bedtime and hot weather, writes the Mayo Clinic. 
Four Phases of CVS
This condition presents with four distinct phases. These include the symptom-free phase — the “interval” phase. This is the quiet period, when the child has no CVS symptoms.
The second phase is the “prodrome” phase, which warns that a vomiting phase is about to start. The child may have stomach or abdominal pain and experiences nausea. This phase lasts from just a few minutes to several hours. If she takes medication early enough in this phase, she may be able to stop an episode before it progresses to the third stage. Sometimes, there is no “prodrome” phase and the child wakes up and begins vomiting.
The third phase, or the “vomiting” phase is marked by nausea and vomiting and an inability to drink or eat. The child will not be able to take any medication without bringing it back up. She is also pale, exhausted and dizzy.
The final phase is the “recovery” phase. The child stops experiencing nausea and vomiting. She regains healthy color in her face, her appetite returns and she regains her normal energy level, writes the National Digestive Diseases Information Clearinghouse. 
No tests are currently available to diagnose this condition (no x-rays or blood tests). Instead, the child’s doctor has to look at the entire constellation of symptoms and the child’s medical history as he rules out other disorders or diseases that result in nausea and vomiting. It also takes time for the doctor to make a diagnosis because he needs to monitor the child through a full cycle of CVS, says the NDDIC. 
Doctors treat CVS in a variety of ways. The syndrome of constant vomiting in children must be treated throughout the entire cycle. During the interval phase, doctors advise the parents of a child with CVS to eliminate known CVS triggers — foods, stress or overexcitement. Children with CVS can also take medications to treat allergies or sinus problems, if these are found to aggravate the condition. The child’s doctor also tells the child’s parents to make sure their child gets plenty of rest and prescribes medication to stop or prevent an episode.
In the prodrome phase, the child can take Zofran or Ativan for stomach pain and nausea. Motrin or Advil can stop any associated pain. The doctor may also prescribe Zantac or Prilosec to reduce the amount of stomach acid the child’s stomach produces.
During the vomiting phase, the child should stay in bed and sleep in a dark room with no noise. If her vomiting is severe, she may be hospitalized and given intravenous fluids to prevent dehydration. She may also be sedated if her nausea doesn’t stop.
In the recovery phase, the child is encouraged to drink an electrolyte replacement solution and water. Depending on how quickly her appetite returns, she may need to stick with clear fluids and resume eating solid food slowly or she can start eating solids right away.
Anti-migraine medications such as Imitrex have not been studied for their safety of use in children, so these should not be prescribed. 
 Cyclic Vomiting Syndrome. Mayo Clinic, retrieved at https://www.mayoclinic.com/health/cyclic-vomiting-syndrome/DS00835
 Cyclic Vomiting Syndrome. National Digestive Diseases Information Clearinghouse, retrieved at https://digestive.niddk.nih.gov/ddiseases/pubs/cvs/