Leto, Anushka was right. If you make your sim sleep hours enough in the cursed sarcophagus, he/she will come out as a mummy, not cursed. The reason you didn't get a mummy, though, is because your sim didn't sleep in there long enough (it's like 30 hours of sleep or something near that, but it doesn't have to be consecutive).
Jancy, at the main menu open the console with ctrl+shift+c, type in testingcheatsenabled true, and then load a game. At your sims' house, hold Shift and click the mailbox. "Make Motives Static" will be one of the options. Remember that using the TCE cheat may sometimes be dangerous if used carelessly.