I've GM'ed a few Pathfinder games, and while I really enjoy the setting, I just can't wrap my head around some of the crunchy mechanics. In particular, how do you (quickly) deal with effects like drain level in a pen and paper system - doesn't each player have to COMPLETELY recalculate their character sheet (feats, spells, skills, BAB) each frickin' time the mummy lord hits them? It seems like that would just grind the game to a smoking halt. How do other GM's handle this?
Negative Levels don't actually reduce your character level
They basically give you a -1 penalty on a bunch of things for each negative level you have.
So you don't actually have to recalculate the whole character, you just have to know what things are affected by level drain, and subtract accordingly. You don't lose any spells, or access to feats, or any skill ranks, etc.
So, really all you need to do is apply a penalty of (negative levels X -1) to all attack rolls, saving throws, and skill checks, and reduce hit points! Spell durations also go down and some other things, but that's not too hard to recalculate on the fly.
This is in contrast to older editions of the game when level drain did actually reduce your character level, so Paizo has baked in to the system a less-crunchy way to deal with the classic level drain problem.
It has been noted that in previous editions temporary negative levels could become actual character level loss. This has also been removed in Pathfinder (this section is right after the previous quote).