Polygraph test?

My SO (significant other) and I have had infidelity/trust issues on both parts. He has scheduled a random polygraph test for the both of us tomorrow. Although I didn't cheat, I know I'm going to fail. The problem is, we have a history of domestic violence. He has blackened and blued me numerous times. If I say no to the test, I'll regret it. If I don't pass, I'll regret it. I know he will pass because he is a narcissistic sociopath and feels no regret for anything he has done. I, suffer from a ton of anxiety. Especially when it comes to the infidelity subject. When he brings it up, my emotions go nuts. I've been tortured on the subject every other day- he insists I'm a cheating liar and If he "finds out" I cheated on him, I "deserve to die". If I don't take it, I'll be "punished". I'm terrified of failing because if the polygraph reading my emotions wrong. What should I do? Do I tell the tester the situation? I have so much anxiety about a false failing that I don't know what to do. I'm a naturally anxious person. I have sever anxiety. Especially with this.
Polygraph test?
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