The most likely culprit is (surprisingly) your own immune system, which works especially hard at night to keep you healthy. But of course, there are a number of other factors that can contribute Nausea is the feeling of wanting to be sick (vomit). Vomiting is when you are sick, or 'throw up'. The contents of your stomach rise up your food pipe (gullet, or oesophagus) and spill out of your mouth or nose. Nausea and vomiting are controlled by a combination of the vomiting centre in your brain, and areas within your gut. Vomiting is the forceful expulsion of gastric contents caused by involuntary contraction of the abdominal musculature when the gastric fundus and lower esophageal sphincter are relaxed. Vomiting should be distinguished from regurgitation, the spitting up of gastric contents without associated nausea or forceful abdominal muscular contractions. Nausea at night can occur for a variety of reasons. Knowing the underlying cause can help guide the treatment. Pregnancy Roughly 75% of people will experience nausea and vomiting while pregnant. It's often referred to as morning sickness, but nausea during pregnancy can occur at any time of the day. bgTYTe.