Heights

Thalia wasn't afraid of heights. She was afraid of the flashbacks. But she let Percy and Jason and the rest of her friends think that to avoid suspicion.

Once while the Hunters were at Camp Half Blood, the Stolls convinced Jason to surprise her by picking her up and tossing her lightly into the air.

She panicked, and struck him and Percy who'd been standing nearby with Annabeth with lightning. She fell to her knees, sobbing and her friends knew she was obviously not okay.

Thalia slipped into the past when Luke and her were on the run, He would toss her into the air without warning, and catch her before she hit the ground. And then they would kiss.

Somethings she never got over.