This is where you fall, in a headstand:dwipada viparita dandasana

This is where you fall, when you drop back your legs in the headstand.

I started on it very early on the mat, because I used to fall a lot then, and still do, from my inversions:)

In this you drop back from the headstand, feet down, and walk the feet ahead, into a plank.

What you need for this pose:

• Strong, flexible neck muscles. 
• A great plank 
• And of course, ability to fall back without anxiety. I remember when I started doing it as an asana (instead of simply falling by accident:) I could not gauge when my feet will hit the ground. Though all of that just takes a few seconds, it seems like eternity, when time goes into an anxious slow mode. Like a slow motion flick.. and this extends your fear and therefore intensifies the contraction, which is going to hurt your neck some time.. So, that phase has to be transited with confidence and awareness. After which it is a cakewalk..
• You can also do this pose from the wheel, though I myself find it a bit awkward. 

Happy sadhana!