Hiatal hernias are pretty common, they occur in roughly 10% of the entire population, with most people over the age of 70 have them. Basically the hernia occurs when a portion of the stomach moves vertically upwards toward the head, placing part of the stomach in your thoracic cavity (where your lungs are).
Hiatal hernias, by themself, are not symptomatic, meaning that most people who have them will never know. Hiatal Hernias are only diagnosed when secondary symptoms appear, mainly GERD (Gastric-esophageal reflux disease). Most people will never develop GERD, but people do. Hiatal Hernias could lead to further problems, only if the GERD goes untreated. If you do find out you have a hiatal hernia, chances are you already have GERD.
Treatment is pretty simple, use drugs to limit the GERD (histamine-blockers, Proton pump inhibitors, or antacids), eat smaller, healthier meals, do not lay down after eating, avoid drugs that irritate the lining of your stomach (ie aspirin), lose weight, stop smoking, and limit stress.