Running a high level D&D campaign has been freaking my shit out for a while now, but the situation has its advantages. For example at the end of last run I announced that the next adventure will take place in a molten lake of magma inside the crater of a volcano. And I'm not sweating about how the PCs will travel on or through the lava. With 20th level spellcasters in the group I just can't be bothered to give a crap about such annoying little details. The players know that there is going to be lava everywhere and I'm totally leaving it up to them to deal with the problem. At this level the DM doesn't need to hold their hands for things like this. If they can't hack it against a burbling volcano, what are they going to do next plot arc when Surtur starts laying the smack down?
"Man, is there anything Jeff CAN'T do when it comes to gaming? This guy is like a critical 20 every roll. Jeff can bite the heads offa five game geeks, including their sorry-ass DM, and spit 'em into a large duffel bag ONE AT A TIME!...that's just the kind of messed up bastard he is! You think yer a gamer, punk? Well..do ya? Jeff will depants your weasel-ass right in front of your grandma."