If you're planning an overseas trip this Christmas (lucky you!) then you should be double checking your passport and any necessary visas round about now. A lost passport will take 10-15 days to replace, so if it's gone missing you really want to find out now rather than the day you travel!
The Age has written up a handy guide of what to do if you lose your passport, which includes contact details for the Australian Passport Information Service. Bear in mind that it costs $200 to replace an adult passport, so it's worth taking the time for a second look before reporting your passport lost.
Passport Panic Stations [The Age]