This also just happened to me. I was in an enclosed building transferring items from one bag to another, completely healthy and I got the "You Are Dead" message.

Apparently, I died from moving my pistol from one bag to another.

30 slot bag sitting on bed moving gear from my 35 slot bag and I got a "You Are Dead" message. Month and a half old character, was quite healthy, not bleeding, not sick or thirsty, just a random death.