What "strange feeling" does Nat have as they run to the theatre?

From the text:

For that moment, though, I had a strange giddy feeling, as if the buildings looming around me were moving, circling. My head was suddenly throbbing. I thought 1 heard a snatch of bright music, from some stringed instrument like a harp or a guitar, and I smelled flowers, the sweet scent of lilies, like in my aunt's garden—and right after it another scent that was not sweet at all but awful, disgusting, like a sewer.