On the train on the way back to Prague, Tereza thinks about the cook at the restaurant where she used to work. He used to sexually harass her all the time at work. She thought of showing up and offering herself to him, because that would mean that she no longer belonged to Tomas.
This was vertigo; her longing to destroy her past.
In this sense, explains the narrator, vertigo is an intoxication of the weak.
But five days after she returns to Prague, Tomas shows up again. She's been waiting for him, but cannot bring herself to tell him this.