Why does Nesta try to go down the stairs in Chapter 8, and how successful is she?

Nesta wants some wine with dinner, but the House refuses to serve her any. She decides to brave the 10,000 steps and go into the city to the nearest tavern. On step 72, she feels dizzy and her stomach churns. Her legs start to shake and her knees groan. She keeps going down to 100. Then at 111, her knees buckle and she nearly falls. The stairwell seems to spin. Her legs tremble so badly, she knows she has to turn around. She forces herself up. She is nearly crawling by the last 30.