fatal error - technical definition

A condition that halts processing due to faulty hardware, program bugs, read errors or other anomalies. If you get a fatal error, you generally cannot recover from it, because the operating system has encountered a condition it cannot resolve. Typically, buggy applications cause fatal errors (fatal exception errors), and the computer locks up. In most cases, all data that you have changed that has not yet been saved to disk is lost.

There is no rule of thumb with fatal errors. You may never get one again, or it may manifest until you fix the problem. If you get a fatal error after just adding a new peripheral or installing a new software package, remove or uninstall it and try again.