Although it is called morning sickness, it can happen any time of the day or night during the early months of pregnancy.
Morning sickness is nausea or vomiting.
Estimates are that only half of all expectant mothers experience the nausea, and only a third of those experience frequent vomiting. It usually goes away by the second trimester, when the level of pregnancy hormones in your body falls. When morning sickness is severe it is called hyperemesis gravidarum. It is not understood why some women develop morning sickness, but hormones appear to be involved. Women with high levels of pregnancy hormones tend to develop this condition and have it in subsequent pregnancies.