The short answer
Seek care if you cannot keep even small sips of fluid down for a day, pass very little dark urine, feel dizzy or faint, lose weight, or vomit blood. These suggest dehydration or hyperemesis gravidarum, which may need IV fluids and anti-nausea medicine.
See morning sickness and after-hours emergencies.
Answered by Dami Women's Clinic (다미산부인과의원), Yeouido, Seoul · Dr. Ko Sang-hyun, OB/GYN. General information, not a diagnosis. Emergencies in Korea: call 119. Medical disclaimer · International Patient Center