There's no one way to handle a member of your family who has become hysterical, just like there's no one reason someone might let their emotions get out of control. However, there are some basic things you can do to respond in a situation where you find yourself confronted with a hysterical family member.
Calm yourself down. It's much easier to reassure someone if you yourself are under control. Take a moment to assess your own emotions, and use the base that you find to reach out to others.
Give your family member a hug, pat on the back or hand to hold to provide reassurance that you are there to help.
Ask the person to slow down and speak clearly. This makes it easier for you to understand the problem and helps the person calm down.
Use a soft, relaxing tone and continual words of comfort to calm your child, parent or other family member into a better state of mind.
Assess the situation and contact emergency services or enlist other necessary help. If the hysteria is over a problem that needs work, talk about steps you will take to make sure everything turns out fine.