HP == Spellpoints is pretty much the Spellpoint Variant: Vitalizing (
from UA, in SRD here), but the spellpoint total
is the caster's HP total. This makes low level casters have more spellpoints, but fewer SP at higher levels. In fact, just using the rules presented under vitalizing, but replacing all instances of 'Spellpoints' with 'Hit Points' does most of what I am talking about. One change that I propose is that all Save DC's and Caster Levels for spells should then be taken from the number of HP spent on them (DC = 10+ 1/2 HP spent, CL = HP spent).
Then we have to actually make exhausted and fatigued matter... to casters since they're likely to be affected by it. veekie's idea about a CL check is good, but I'd like to see if we can make a Concentration check a valid test.
[direction shift] Rather than fatigued and exhausted, if you're under, say 50% HP, you're
Sickened, and perhaps w/o the Endurance feat, you're
Nauseated at < 25% HP?
I haven't seen any creature that has immunity to being Sickened or Nauseated, only immunity those forms of it that come from a disease poison or necromancy effect. This is not a poison or disease effect, so a lich can be sickened, a golem can be sickened, etc.
How about it? [/direction shift]