My tail lights failed on a trip at night. What causes this? Light switch? on 2006 Cadillac SRX

Returning last night from a holiday trip, my tail lights would not operate. This happened before, several weeks ago, and I simply turned the light switch (turn signal column) until they worked. This simple remedy did not have any effect last night, and we had to drive 200 miles with the emergency flashers on to reduce the possibility of being hit from the rear, in the dark.

Asked by for the 2006 Cadillac SRX