Getting a little up-tight and nervous is normal, especially for children. Even for adults, the situation brings some uncertainty. The up-tightness is part of getting ready to deal with whatever happens. Nonetheless, if your child noticeably reacts like this with regularity, it signals a possible problem. This is especially true if he gets more upset than the person to whom he is reacting. If he has the reaction when the anger had nothing to do with him, it is a bigger problem. When he reacts just because he thinks someone might get angry, the problem is even worse.
What is happening? Your child is overreacting. Why? Because he fears something very bad is about to happen, and probably to him. Children behave like they have learned to behave. This is especially true for their emotional reactions. Your child is afraid and fears he or someone else is going to get hurt.
Helping your child with this sign is not complicated but takes a long time. Your child needs to learn people get upset and angry at times; but this does not mean someone is going to get hurt or anything bad will happen. Talk with him about his fears. You can say, "You feel upset. I think you're reacting to someone else's anger and nervousness. It feels like you're afraid you or someone else might get hurt. It doesn't work that way in our family. We all get angry at times. You can get angry too if something upsets you. Getting angry is okay. This is the difference. When we get angry, we talk to each other. Sometimes it gets a little loud; but that's as far as it goes. We don't hurt each other. Let me know the next time you get angry about something. That is part of how we know what everyone in our family is thinking and feeling."
Be sure what you say is true. Insist no one hurts anyone at your house. This includes how the adults relate to each other, how you handle your anger and frustrations, and how you express your negative or unpleasant emotions. This again emphasizes the importance of parental modeling and the example you set for your children and the example they set for each other.