I've had this happen several times, with different sims. Sometimes they get thrown entirely out of the tomb, and sometimes just a little ways away into another room. I usually use the testingcheatsenabled teleport cheat to get back to where I'm supposed to be. I only mention this because if you do that, you probably need to have your sim go back and finish sleeping, or click your sim and choose "Wake Up" -- I've had them walking around doing things, and then discovered they were unable to interact with anyone, and it's because the game still thinks they're asleep! If you use resetsim you probably wouldn't have the sleeping problem.