I'm just waiting to be hit...
My shoulders are hunched and I'm making as little noise as I can while typing away on my computer. When my husband walks into the room, I roll my chair back so that I'm out of his way. Facing him, but sitting very still, and making no eye contact. I wait for him to indicate what he wants.
No, it's fine; he just came into the kitchen to refill his glass of water. He does that, and then heads back to his office. Some of the mental alarms quiet down, and I can relax a little and go back to work. But I'll still keep an ear out for any threats.