• Dehydration - The body loses water rapidly due to excessive vomiting. Severe dehydration cases may be treated in the hospital.
• Food tube (esophageal) injury or Esophagitis - The tube that connects the mouth to the stomach (esophagus) may be harmed because of the stomach acid that is thrown up during vomiting. 
• Dental caries - The acid from the stomach can corrode and decay tooth enamel.

Click here to learn more about complications of CVS: https://www.niddk.nih.gov/health-information/digestive-diseases/cyclic-vomiting-syndrome/definition-facts