Haha we've all probably been here once or twice! Increase the detail size in your dyntopo settings; try 10 or 15. Then lightly touch the spot with a brush (any generative brush, but try inflate). The light touch(es) should generate new topology for that mess, which should 'reset' that geometry effectively. Then you can re-sculpt that area the way you like, stepping back down the detail size as needed.