Can a hiatal hernia be fatal?

Essentially No: Unless the hernia is so large that nearly all the stomach is in the chest and a gastric volvulous occurs (rare) needing emergency surgery. Heartburn ; reflux symptoms are usually treated medically. Elective surgery for some situations. Be sure you see a doctor for the proper testing.

yes, but rare: Large hiatal hernias, also called paraesophageal hernias, can cause the stomach to twist to the point that the blood supply is cut off, and the stomach turns in to gangrene. Catastrophic bleedng can also occur, be this is even less likely. The risk of this happening is probably less than 5%, but it is unpredictable. Small hiatal hernias are not dangerous at all.