Unexplained nausea can have so many causes. It can be a symptom of various undiagnosed diseases, a side effect of medication, or the first sign of a food allergy. Other times, the stomach is not receiving the nerve signals it needs in order to commence digesting properly.
Diagnosing nausea begins with eliminating the most common causes. If someone is on a certain kind of medication, they may be asked to go off it in order to discern if nausea is a side effect. Pregnancy and hunger are also causes of nausea that can take someone by surprise. Once these options have been ruled out, the doctor may ask the patient to keep a log of all her daily activities in order to determine the cause.
There are several chronic illnesses which have continual nausea as a little-known symptom. For example, diabetes can begin with nausea before any other obvious symptoms. Problems with the gallbladder can manifest themselves in a queasy stomach as well as a pain in the side. Acid reflux disease can have nausea as a main side effect.
Unexplained nausea can also happen as the result of a food allergy. Though food allergies are usually diagnosed when people are children, they can also develop later in life. Sometimes, a person will become allergic to a food he previously had no problems with. In these cases, a patient is often asked to start as bland a diet as possible, then keep a food diary as they add new items to the diet. When the person has a reaction to a new food, he will have found the cause of his unexplained nausea.
Nausea associated with chronic conditions can be misleading, because in absence of other symptoms, the main problem will seem to be gastric, rather than the symptom of a larger problem. Making an appointment with a doctor and working with a gastric specialist can help a sufferer sift through all of the probable causes to find a treatment.
Finally, unexplained nausea may not be caused by a disease or a food allergy, but by a nerve disorder. Some researchers refer to the stomach as having a "pacemaker," meaning that it receives nerve signals telling it whether or not to digest. Sometimes, the stomach can receive these messages when they're not needed or never receive them at all. When the stomach is "paralyzed" like this and unable to digest food, the patient often feels sick to her stomach. Treatments for this type of stomach problem are still being researched.