Irrational Fears

Irrational Fears are illogical fears that most demigods are sometimes plagued by. Demigod fears are often based off of their parents' stories or sometimes in traumas they had when they were young. They are caused by Phobos, as shown in The Demigod Files.

Children of Aphrodite
The demigod children of Aphrodite are afraid of not looking perfect all the time, or they have a mild case of Cacophobia (fear of ugliness). They are also afraid of not being fashionable.

Children of Athena
The demigod children of Athena have Arachnophobia, the fear of spiders. They fear spiders because of the story of Athena and Arachne. This is because Arachne's children seek revenge for their mother. Annabeth's fear of spiders shows itself many times during the original series.

Children of Hephaestus
The demigod children of Hephaestus have Acrophobia, a fear of heights. It is because their father Hephaestus was pitched off Mount Olympus by Hera (who blames Zeus) as a baby. It is mentioned in The Ultimate Guide. This is strange because Leo Valdez, a known son of Hephaestus, flew the Bronze Dragon, Festus. Also, Charles Beckendorf flew Blackjack in the beginning of The Last Olympian.

Children of Poseidon
The demigod children of Poseidon have Claustrophobia, a fear of confined spaces. It is because the sea is so open, free, and wild. Percy mentioned his claustrophobia in The Lightning Thief, but it doesn't seem to bother him in The Battle of the Labyrinth. It could simply be that they become restless when confined, but are still functional and it only acts as a mild annoyance, or it may be a mistake of the author.

Satyrs
Satyrs are afraid of caves and underground locations. This is because they can't tell if there are monsters nearby, as the underground smells like monsters.

Clarisse La Rue
Clarisse's greatest fear, as mentioned in The Demigod Files, is her father Ares threatening, scolding, and punishing her.

Grover Underwood
Grover Underwood has a fear of Cyclopes and is afraid he will be eaten by them. It can be traced back to when he was leading Luke, Thalia, and Annabeth to Camp Half-Blood, but took some wrong turns in Brooklyn and got trapped in a Cyclops' lair. Then, there was the time Polyphemus was going to eat Grover. Grover had problems with Tyson, and the feeling was mutual, but they both eventually got over this. Grover also has a fear of rabbits which Thalia calls his "bunny-phobia." Grover mentioned that bunnies "steal carrots from defenseless satyrs."

Percy Jackson
Percy Jackson is afraid of the Great Prophecy. It is shown in the The Demigod Files story, Percy Jackson and the Stolen Chariot, when Phobos makes Percy see his worst fear. It is unknown if he has a new fear after the Great Prophecy finished.

After nearly dying in a muskeg in Alaska, Percy develops a fear of suffocation so intense that it actually makes him wary about traveling underwater, despite the knowledge that he can breath underwater. As The Mark of Athena progresses, Percy comes to believe that his fear is not just of physical suffocation, but being "suffocated" by the burden of responsibility for his friends' safety which he places on himself. However, he does start to overcome this fear later in the book.

Tyson
Is afriad of sphinx due to attack when younger. Also satyrs due to allergies

Thalia Grace
Thalia Grace has Acrophobia, a fear of heights, as shown in The Titan's Curse. Percy finds this ironic because Thalia is the daughter of Zeus, the god of the sky.