Stress
Mental and emotional stress are part and parcel of international aid work. You may see things that you aren't prepared for: children starving, men and women dying, abject poverty, deadly illness, and terrible violence. You may find yourself in a situation, say, following a catastrophic earthquake or typhoon, where saving lives means that you get less than the absolute minimum of sleep to maintain standard function for an extended period of time.
Even if your assignment doesn't involve danger or disaster, this job can drop you in the middle of a foreign country with a language and culture that are completely unfamiliar to you. You won't see your family or friends back home for months at a time, and there's a possibility that you won't be able to speak to them via phone or email, either.
Of course, making your way in the world without having to interact with your parents on a regular basis may be one of the reasons you're interested in a career as an international aid worker in the first place. We don't judge.