Unfortunately, this can happen - and a number of things can cause it. Your sewer lateral (the connection from your house to the city sewer) can back up - from tree roots, excess paper, a pipe not pitched correctly etc. The city sewer can back up - tree roots, grease, unknown objects that can then clog back up all the way into your house.
What do you do in this situation? First step, try not to panic. Second step, call Top Tier - we're on call 24/7. We can come out and get the blockage unclogged. Once the blockage is unclogged, we can televise your line to help diagnose the cause of your problem. If you have experienced recurring sewer clogs in the past, give us a call to televise your line to see what has been causing your issues.
Here's hoping you never have to experience the "horrible, awful" - but in case you do, remember to turn to Top Tier.