The candidate`s team said she was diagnosed with pneumonia on Friday and given antibiotics, but had become dehydrated at the New York event.
Her doctor said she was now re-hydrated and "recovering nicely".
Mrs Clinton was due to leave for California on Monday morning for a two-day trip that included fundraisers and a speech on the economy.
Her personal physician, Dr Lisa Bardack, said: "Secretary Clinton has been experiencing a cough related to allergies. On Friday, during follow-up evaluation of her prolonged cough, she was diagnosed with pneumonia. She was put on antibiotics, and advised to rest and modify her schedule."
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