You have never seen me un-calm. But profanity in the morning makes me cranky.
Tell me:
What version of DB you are running.
What happens. Is it a crash? (You should get a popup with a error message or error code at minimum) or is it a hang? (program stops responding, window won't refresh, etc.).
When does it happen? I.e. how long were you running before it happened, can you make it happen by doing something, etc.
Posting the sim helps me with settings, bots, etc.
From what you have said, it sounds like a tight loop hang. These can be hard to reproduce. One thing you can do is use the autosave feature to save your sim every 5 minutes or something. Then when it happens, re-load the last save and see if it happens sooner. If it does, post that sim and I will be able to reproduce and fix it.