Considering the fact that almost half of all pregnant women experience some form of morning sickness, it's not surprising that some of these will be extreme cases.
Women who are afflicted with severe morning sickness generally experience many symptoms that can become painful. Dealing with these symptoms is very important in order to prevent further more complications from developing. Morning nausea alone can be difficult but severe morning sickness is worse. There are a variety of reasons why some pregnant women have a harder time. Some of those afflicted with extreme morning nausea, go on to be diagnosed with hyperemesis. The relationship between hyperemesis and morning sickness becomes clearer.
http://healthmagazinehouse.com/severe-morning-sickness/