I just wanted to post a video I encountered recently that highlights the single most important rule in flying – always fly the airplane. The video shows a pilot/flight instructor who apparently faints or becomes otherwise incapacitated. Unfortunately, the guy in the back appears to take that as a cue to freak out and scream rather than take over flying. There are some questions as to whether the video is staged, but it offers a good example regardless.
What the guy in back should do, rather than screaming and freaking out is calmly take control. Apply throttle and level out the plane. Then he can deal with the dead/passed-out/etc instructor.