Unfortunately I don't have my PHB handy, nor do I have a DMG so I can't check the negative level description there, but the special abilities section is one of the released parts of the SRD, so in theory it should be an authoritative source.
Hypersmurf said:
PHB Glossary - no mention of hit point loss.
DMG Special Abilities - no mention of hit point loss.
MM Special Attacks - no mention of hit point loss.
CRGreathouse said:The second printing of the PH includes the -5 hp in the back.
Alright, so it appears that negative levels are supposed to inflict damage, now the question is whether or not negative levels inflicted by Enervation also inflict this HP damage.