1999 Chevy Suburban Car shuts down

With increasing frequency, the car shuts down completely and will not restart. There is no spark, even though the battery checks out at 12.5V. None of the warning lights, lights, or other electrical devices work either. After a few minutes, everything is restored. The car starts up and drives fine. This has happened twice in a parking lot and twice on the highway. Thankfully, both highway incidents recovered immediately and restarted on their own.