YOU MAY EXPERIENCE INCREASED APPETITE
Or find that you're ravenously hungry, 24 hours a day. Set up shop in the kitchen or bathroom and grab the phone book. Fundamental incompatibilities with your native biochemistry may require you to consume an entire pepperoni pizza every 15 minutes or so. You may also see some blood in the copious, toxic, slimy purple stool your body will begin to produce-but don't worry, it's entirely your own.
PREPARE YOUR HOME
Invite friends over for an "alien shower" and ask them to help you cover any valuable possessions in plastic sheeting. You may wish to attach a tag to each item, denoting its intended recipient. For extra fun, will the most desirable objects to people who've snubbed your invitation, so they will be more likely to visit once you're gone and provide nourishment as the little one gains incredible strength and power.
For your time as a warm and loving host organism will shortly and abruptly be coming to an end. The extraterrestrial creature nestled softly among your vital organs is just about ready to gnaw its way into the next phase of its amazing and wonderful life cycle. Membranes, tendons and bones that once seemed like impenetrable barriers are now mere appetizers in the path of your eager visitor.
Relax and let nature take its course. You'll feel something like heartburn, followed by a minor heart attack, shortness of breath, and a wave of aneurysms. The most difficult part is now over, so just open your eyes and relax, as an explosion of blood and flesh lets you know you've succeeded in passing on the sacred baton of Life.