Water Heater Sediment

I had a sudden burst of sediment out of my water heater to the fixtures in my house. They are white and gray rocks/flakes. It clogged up the hot side of all of my sink fixtures. The tub fixtures did not get clogged up, so I was able to see what the sediment is. I have an 80 gallon electric water heater. It is about 8 years old. We have never had any issues with hot water temperatures or quantity of hot water. I can't figure out why this suddenly happened. Is it possible that my water heater is hooked up backwards,so the water is leaving the WH from the bottom where the sediment is? I drained my WH last year, so the sediment must have come from the city main suddenly also. Any help is greatly appreciated.