While /die will work, another thing to try is to quit and relog. Sometimes it will then "let you off the wall".
I had a particularly laggy day ... ran from Hydlaa out to BD and (because of the lag) got stuck in the wall halfway up the canyon. There were no GMs on and I really didn't want to face going through DR and all the way back up to BD, so I logged out. When I logged back in later, I was able to walk off the wall.