Nervous stomach is an old-fashioned term for chronic indigestion. The idea of having a nervous organ could be a holdover from about 100 years ago, when a syndrome called nervous exhaustion or neurasthenia — thought to be caused by "nerve irritation" — was a fairly common diagnosis. The typical treatment was a long period of rest.
Today, it would be unusual for a doctor to say you have a nervous stomach. That said, your nervous system can definitely affect your digestion. In fact, some functions of your nervous and digestive systems are so interdependent that they're thought of as a unit — the brain-gut axis. Your digestive tract also has its own separate nervous system, known as the enteric nervous system, which operates independently of your brain to regulate certain aspects of digestion.
The brain-gut axis could be involved in the chronic digestive problems known as functional gastrointestinal disorders, including irritable bowel syndrome, functional dyspepsia, and functional abdominal pain. These conditions aren't the result of a structural abnormality or infection in your gastrointestinal tract, but they can take a serious toll on your quality of life.
If you have a recurrent digestive problem, tell your doctor what it is — stomach pain, heartburn, bloating, diarrhea or several symptoms at different times. You'll also need a physical examination, possibly followed by tests to diagnose or rule out an ulcer, gallstones or any other specific disease your symptoms suggest.
This workup may not identify a specific abnormality. If you're otherwise healthy, though, further testing is usually unnecessary. Instead, your doctor may suggest that you keep a symptom record and track your diet, mealtimes, stress levels and other variables that may be triggering your problems. This record may highlight a few simple changes you can make to reduce the frequency of your symptoms. A combination of lifestyle adjustment, medication and behavioral treatment usually brings functional gastrointestinal disorders under control.