Cyclic vomiting syndrome (CVS) is a pattern of repeated bouts of severe nausea and vomiting usually interrupted by even longer periods without symptoms. Symptoms occur suddenly and may last for hours or even days. In the worst cases, patients may vomit between five and 12 times an hour for up to 10 days.

CVS unfolds in four phases:

• Prodrome. A patient experiences abdominal pain that may last for anywhere from a few minutes to several hours.
  
  
• Episode. The patient experiences nausea and vomits repeatedly. The patient may also gag and experience listlessness and have unusual skin paleness.
  
  
• Recovery. During this phase, the patient ceases vomiting and nausea subsides.
  
  
• Symptom-free interval. This is the phase between episodes in which no symptoms of nausea or vomiting are present.

Children are diagnosed with CVS more than any other age group. It is most likely to affect girls between the ages of 3 and 7 years. Adults can also have this condition, and tend to experience episodes that are less frequent but more intense than those of children with CVS. In children, CVS often subsides before the teenage years. Some children with CVS develop migraines later in life.

The exact cause of CVS remains unknown. However, there appears to be a relationship between migraines and CVS and some research suggests that the condition is also related to panic attacks (sudden episodes of fear and anxiety). Infections are the most common trigger of symptoms, but children are also susceptible to vomiting cycles after experiencing emotional stress or high levels of excitement. Eating too much food or certain types of food also tends to cause symptoms in some patients.

Diagnosis of CVS is complicated by the fact that many other illnesses and disorders can sometimes cause vomiting. CVS cannot be diagnosed until these other disorders – including stomach flu and food poisoning – are ruled out.