Shoulderstand:
http://www.santosha.com/asanas/sarvanga.html
I find it tricky to keep my feet straight up instead of leaning back over my head, the longer I hold this pose.
I've heard of that approach for headstands, and I've tried it, seems like it would work if I practiced more! I've also tried doing headstands against the wall. One of my main problems with them is that I can't stand pressure on the top of my head. But perhaps I'm just not resting the weight in the right place.
"Sort of yoga class"? Do tell!