I actually got out of this exact place manually. Try crawling to the South-east corner closest to the ground, wiggle around a bit and try to make your head stick out of the floor. Once you have done so, log off and switch server. This is what I did and it magically spawned me back on the normal ground. (If you are on a private hive merely logging off and trying to spawn on ground level probably will not work, since I tried this also on the same server. Only after I switched server I ended up above ground)