Its a glitch when you get knocked through the ramps as opposed to off them. You can get back out in 2 steps.
1) Target someone in the group by clicking on their portrait in the group window.
2) Then type /follow
It should pull you up out of the pit and you should be on your way. Someone will have to be around that area for it to work.
Interesting. I haven't tried this command. How well does it work for say... not getting turned around your first time in Story Mode with the group?