This mod was born out of my perception that The Sims 4 is not nearly as chaotic as the previous installments, which I loved and miss very much.
In an attempt to shake things up a bit (or a lot, depending on your preference), this mod adds a new death type:

Sims from Teen to Adult can also randomly die peacefully in their sleep — just like Elders.

How it works

When dying in their sleep, Elder Sims still die of Old Age, handled entirely by the game. This mod only adds new triggers to it; nothing else about the "Pass On" Elder death changes.
Teen to Adult Sims die of Sudden Death, a new death type that's based on the "Pass On" death in the Life & Death EP.

Each age group has its own chance, defaulting to 0.5% (Teen), 1.0% (Young Adult), 1.5% (Adult), and 2.5% (Elder) per roll (default is every 2 hours of sleep).
These settings can be changed on the .cfg file or by cheats. Setting a chance to 0 disables the mod for that age group.
Death chance is increased or decreased by a few factors:
- Chased by Death trait: Increases chance
- On Thin Ice buff (triggered by the Chased by Death buff): Increases chance
- Getting a Reversed Magician tarot card: Decreases chance

Only Sims in the active household you're currently playing can die this way — townies are never touched, and pets are never affected either.

Every existing death-prevention/immortality settings and features are still respected.

A note about Rebirth

Life & Death EP's Rebirth feature bugged out a bunch of times during testing, with and without the mod. From what I could gather, that's a game bug this mod can't fix.
When a Sim dies, I recommend choosing "Playable Ghost" or "Freeroaming Ghost" to avoid that bug.

Requirements

Script mods enabled
Keep HNRY_SuddenDeath.ts4script, HNRY_SuddenDeath.package and HNRY_SuddenDeath.cfg in the same folder inside your Mods folder.
Optional: Life & Death EP.
- When installed, a Sim dying in a bed uses the pack's Pass On animation. When it's not, every sleeper gets up and uses a base game animation instead.

Drop the three files in Mods folder (ts4script, package, cfg). When updating, you can keep your existing HNRY_SuddenDeath.cfg. Fully quit and relaunch.

Cheats

hnry.sd.status — Show current settings and stats
hnry.sd.chance — Show every age group's chance
hnry.sd.chance <age> — Show that age group's chance
hnry.sd.chance <age> <percent> — Set that age group's chance (0-100)
<age> accepts teen, young_adult, adult, or elder
hnry.sd.interval <hours> — How often (in-game hours of sleep) chances are rolled (0.25-24)
hnry.sd.enabled 0|1 — Turn the mod on or off
hnry.sd.reload — Reload settings from the cfg file
hnry.sd.force — Immediately kills the active Sim in their sleep: Sudden Death for a Teen through Adult, Old Age for an Elder. Requires the active Sim to be sleeping.

Compatibility

Not compatible with any other mod patching SI_DeathInSleep_Start,
death_Elder_DeathInSleep, or death_ElderExhaustion directly.

Disclaimer

This is one of my first attempts at Python coding/modding. The mod itself is liable to bugs, as most are. Please make a backup of your save before installing.

Support

For bug reporting or support please contact me on Discord @henryvotril

Thank you for using my mods! 💕

Sudden Death — younger Sims can also die in their sleep