With no warning my mom sims died of laughter. I am so mad.

I hardly ever notice this feature. Avoid the goofball trait and send your sims to a mirror to calm down if they become very playful. It gets critical if they become hysterical. Also, pay attention to any items with enabled emotional auras. Emotional deaths have been a thing for a very long time, so it shouldn't come as a surprise that they can happen.