At 5 minutes and 36 seconds of lecture, the plane is much bent but I am flat. I followed the lecture exactly. Version 2.78. Why?
Try adding a solidify modifier.....not sure whether that was intended but it seems to work!
Solidifier worked for a while but resulted in holes and gaps in the mesh...I did not apply it...
When I removed it my plane acted how it was supposed to in the tutorial...
Try adding solidifier and then after tweaking a few settings and adding force field ....remove it...
Sometimes "weird" works...