You're doing what you love, and hey—you're taking pictures, for goodness sakes. Most of your stress will come from having to pinch every penny. Although if you're cruising other continents and climates for National Geographic, you might also have to watch out for Somali warlords and other hazards that pop up along the way.
Those weekly phone calls from your mother can also be stressful. "Are you still taking photographs?" "Have you gotten a real job yet?" "Your brother was just named Employee of the Month at his fast food restaurant—am I ever going to be able to be that proud of you?"