Final answer:
Hyperemesis gravidarum is the severe form of nausea and vomiting that can occur after week 16 of pregnancy, causing more extreme symptoms than morning sickness.
Step-by-step explanation:
The severe form of nausea and vomiting that occurs after week 16 of pregnancy is known as hyperemesis gravidarum. This condition is characterized by persistent and severe nausea and vomiting beyond the first trimester, which can lead to dehydration and weight loss. These symptoms are much more extreme than the common "morning sickness" experienced during the first few weeks to months of pregnancy due to increased pregnancy hormones. While morning sickness tends to subside by about week 12, hyperemesis gravidarum occurs later and is much more severe.