Following a performance Monday at Santa Monica Place mall, Gomez told Us Weekly: "I was just very malnourished. I was low on iron and exhausted."
The performance in Santa Monica had originally been scheduled for last Friday, but was postponed when Gomez became ill.
People.com reports that Gomez told the 3,000-plus crowd assembled on Monday: "I want to thank you so much for coming. If you guys came on Friday, I'm so sorry that I couldn't be here. ... I love you guys very much." According to People, she appeared in good health and also told the crowd, "I do feel better."