Lee's rep tells PEOPLE that she remains hospitalized in New York City after experiencing "a heated feeling" and "tightness in her chest."
Lee's partner, New York Gov. Andrew Cuomo, left Billy Joel's final concert at the soon-to-be-closed Nassau Coliseum on Long Island and rushed to her side at the time of the incident.
At the hospital, Lee is receiving antibiotics for a fluid build-up, her rep says, and "will be monitored for a few days." She is resting comfortably and "is anxious to recover," the rep says. "This has been frustrating."
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Lee, 48, underwent a double mastectomy in May after being diagnosed with a common form of breast cancer, DCIS (ductal carcinoma in situ) in March.