I heard this expression used by our English trainer before.
He popped a question that made everyone apprehensive to answer. And there was a long space of silence. He then said, ¨You look like a deer in the spotlight.¨ - What does it really mean and do you use it often
Usually we say a "deer caught in the headlights," not spotlight. When a deer dashes out from the woods into the road and into the path of an oncoming car, he is temporarily blinded by the headlights. He'll stand there frozen in terror for a moment or two and either run off or crash through your windshield.
Maybe that´s it. For I heard it long before I even thought of learning idioms. I just took it from my memory.