FMLA leave is limited to “serious” health conditions. This means an illness, injury, impairment, or condition that involves inpatient care or continuing treatment by a recognized health care provider. An employee need not be physically unable to work. An employer may require certification by a health professional, second or even third opinions at the employer’s expense, and re-certifications on a reasonable basis. Leave may be intermittent when medically necessary and not unduly harmful to the employer’s business. Employers may require, or employees may elect, to use up paid leave first.