I sent a Phantom through a hole in the canopy for some shots of the redwood forest from above. It was actually a little scary—no wind in the forest, but lots of wind above it. During one flight from a clearing, the Phantom lost GPS. The light on the back turned yellow, and no amount of toggling GPS/Attitude would bring it back into GPS mode. It felt like a flyaway until I realized what was going on. Upon landing, I cycled power, and it now seems to work in GPS mode, again.

Make sure you are a competent pilot in Attitude mode so you can recover from this sort of thing!