As a DM, I have never liked Energy Drain. Though I do understand the harshness inherent in the game, I thought that energy drain was a bit too harsh. Even instant death poison allows a saving throw, after all. Many players and gamers have expressed to me over the years that the loss of more than one level due to energy drain is almost a fate worse than death.
The mechanics of energy drain always seemed a little metagame for me. I don't like that they steal a level, because what does that really represent, especially in a game where the classes have very different experience tables? Does a thief have "less life energy per level" than a fighter? It just doesn't sit right with me.
I am presenting my house ruled version of energy drain. In some ways, it is actually more serious than the previous level loss, but at the same time, it fits better with my conception of what "draining life energy" means.
Revised Energy Drain--
When a character is stricken by a creature or spell that causes energy drain, they lose one hit die; the character rolls a hit die and permanently loses that many hit points. In addition, they are forever after considered as being one hit die less. (But not class level) The only ways to restore life energy thus drained is a restoration, wish or other, similarly powerful magic.
At the DM's option, a saving throw may be allowed for losing half the amount of hit points rolled on the die.
In addition, the ripping away of one's life energy is a traumatic process, and the individual is often no longer the same. If a character is drained, have the player roll 1d10 and consult the chart below:
1 The character gains a random, permanent insanity
2 The character ages 1d4x10 years
3 The character loses 1 point from all attributes permanently
4 Roll a d6. 1-2 loses 1 point of Int, 3-4 1 point of Wis, 5-6 1 point Cha
5 Roll a d6. 1-2 loses 1 point of Str, 3-4 1 point Dex, 5-6 1 point of Con
6 The character is haunted by nightmares. Each night there is a 10%
chance that he does not benefit from the night's sleep.
7 The character develops a severe phobia of undead and will not fight them
8 The character always feels cold, no matter what the weather.
9 The character's hair turns stark white
10 The character gains a shock of white hair.
Note that these effects are permanent until the character life energy is restored. Generally, a DM should only impose one such roll on the player, unless they lose 25% or more of their levels in a given encounter, in which case a second roll is warranted.
If the DM uses saving throws as above, he may opt to spare the player a roll on this table in the event of a successful save.