If they're newlyweds or have a new baby, all they have to do is go into a room with someone with whom they have "let the good times roll!" playful sentiment. I had a mom with the Cheerful trait who kept keeling over because... she liked her daughter. She would also autonomously take bubble baths and die.
Don't worry people. The sims are just becoming sentient beings, and are simply looking at all the glitches in the game and just can't help but die of laughter.
In all seriousness, I just have the base game and Kids Room stuff and there have been way too many times lately where I need to rush my sims to a mirror to calm down. I had one situation where I was so worried about my sim dying that I made a backup save while they were hysterical. They didn't seem to want to do the interactions I was telling them to do, they kept cancelling them out for other things (which is extremely annoying in other cases but was even more so here), and I thought for sure they were going to die. In my case it also doesn't seem to help that if I have a tub on the lot my sims only seem to want to autonomously take a bubble bath, add that with watching comedy on TV and the many other things that give a playful mood and it's really annoying.
I'm sure some may disagree with me, but the moods in this game are just one more thing that I wish had an option to be disabled. That, plus the story calls and the sentiments can all go dive off a cliff if you ask me lol.
I'm running 2 identical saves to stop losing my Sims after one laughed herself to death on her honeymoon in the jungle with absolutely nothing funny going on...like at all, one minute it's honeymoon french toast and the next minute giggles, chuckles, laughter, hysteria and thud. Followed by Saffron honey are you okay? Saffron? Noooooooo! Thank goodness for death flowers, but now you need 2 people to use a death flower unlike in previous games where the deceased Sim just handed it over.
It literally just started happening in the last 6 months or so.
