Tereza would have done anything for her mother's love.
Now that she was with Tomas, she got letters from her mother regularly, and they made her want to return home. This is her vertigo, her desire to fall.
When Tereza finds out that her mother has cancer, she is even more angry at Tomas; she feels as though she's abandoned her mother for a man who doesn't even love her enough to be faithful. She prepares to take a trip to see her mother.
But Tomas, being a doctor, does some hunting around and discovers that Tereza's mother does not have cancer. He stops her from going on the trip.
Tereza begins accidentally hurting herself by tripping or falling; this is a manifestation of her vertigo. But Tomas always picks her up.