A hiatus hernia or to refer to its medical name, a gastro-oesphageal reflux disease, happens when a part of the stomach protrudes through the diaphragm at its weakest point (where the oesophagus passes through the abdominal cavity).
A hiatus hernia is different to other hernias, in the sense that it cannot be seen externally and often people do not have any symptoms.
However, those who do, like yourself, can try to lose some weight (if you are overweight). You should also stop smoking. Try not to lie down or bend after eating for at least 30 minutes after a meal. Also always eat small meals, if necessary four or five small meals per day rather than two or three large meals.
If the symptoms you are experiencing are particularly troublesome, then it may be worth talking to your doctor about having some kind of drug treatment, such as omeprazole.