However, the character does get a Fortitude save 24 hours later, assuming he lives that long:
Energy Drain (Su) This attack saps a living opponent's vital energy and happens automatically when a melee or ranged attack hits. Each successful energy drain bestows one or more negative levels (the creature's description specifies how many). If an attack that includes an energy drain scores a critical hit, it bestows twice the listed number of negative levels. Unless otherwise specified in the creature's description, a draining creature gains 5 temporary hit points for each negative level it bestows on an opponent. These temporary hit points last for a maximum of 1 hour. Negative levels remain until 24 hours have passed or until they are removed with a spell, such as restoration. If a negative level is not removed before 24 hours have passed, the affected creature must attempt a Fortitude save (DC 10 + 1/2 draining creature's racial HD + draining creature's Cha modifier; the exact DC is given in the creature's descriptive text). On a success, the negative level goes away with no harm to the creature. On a failure, the negative level becomes permanent. A separate saving throw is required for each negative level.
Format: energy drain (2 levels, DC 18); Location: Special Attacks and individual attacks.
It's not entirely clear whether the character makes one saving throw per negative level or one saving throw for all of the negative levels, so expect different answers there.
On a related note, I learned something today: Never, ever get critically hit by a vampire. O_O