Tom, do you remember the scene from the original ALIENS movie when the thing burst out of the guy's chest? That's NOT going to happen to you, but if you don't get them treated you will have a fly emerge from under your skin!
It's not fatal, or even terribly dangerous to humans - the only symptoms are some pain when the larvae moves (yuk!)
The Bot Fly lays its eggs under the wing of a mosquito. The eggs are heat sensitive, so when the mossie lands on you, the eggs detach and beging to burrow into your skin. They have hooks around their mid-section which means you CANNOT pull them out. Ingeniously (and this is why you don't get infections) they release their own antibiotic so they don't get rejected.
They breathe through a hole in the bit sticking out, which is why when you go swimming or shower they hurt - the larvae is drowning and moves around!.
Remedies - and I'm not advocating any of these, just telling you what people say works, let the medical staff handle this - include super-glueing the mouth shut. You still have to remove the dead larvae the next day. Some say you can put a piece of meat on your leg, and the larvae will burrow up into that instead of your leg.
The doctors will probably apply an anaesthetic, make an incision and remove the larvae. You should heal up without any scars in a week or two.
Moral of the story: wear insect repellant! about 7 years ago