What's with the sudden nausea?

Sudden nausea may be caused by pregnancy, digestive system diseases, and central nervous system diseases, as follows:

If a woman has unprotected sex before pregnancy, hormones in the body will rise, causing nausea and vomiting. Clinically, it may also be digestive system diseases, such as gastritis, enteritis, duodenal ulcer, food poisoning, etc., and the stimulation of bacteria causes gastrointestinal discomfort. Secondly, it is also necessary to consider central nervous system diseases, such as meningitis, hypertensive encephalopathy, which will lead to abnormal control of the central nervous system and nausea.