tremendous lag + disconnects in dungeon

After a few weeks of play with pretty much zero lag issues, my first dungeon run featured several instances of extreme lag (skill delay, skills not firing, PCs/NPCs freezing then warping around, etc.), plus 3 times where I was disconnected from the server and dropped back to the start screen. I was able to log back in each time within a couple minutes, back in the same party, but obviously vanishing from the group mid-fight isn't the best situation.

Anyone else encounter this issue before? Any ideas for troubleshooting or avoiding this in the future?