No. According to the EEOC, granting leave to an employee who is unable to provide a fixed date of return may be a reasonable accommodation. Although epilepsy often can be successfully controlled, some individuals may need to take extended leave because of the frequency or severity of their seizures and may be able to provide only an approximate date of return (e.g., “in six to eight weeks” or “in about three months”).
In such situations, or in situations in which a return date must be postponed because of unforeseen medical developments, employees should stay in regular communication with their employers to inform them of their progress and discuss the need for continued leave beyond what originally was granted. Employers also have the right to require that an employee provide periodic updates on his or her condition and possible date of return. After receiving these updates, the employer may reevaluate whether continued leave constitutes an undue hardship.
Source: EEOC Publication: Revised Questions and Answers about Epilepsy in the Workplace and the Americans with Disabilities Act, http://www.eeoc.gov/laws/types/epilepsy.cfm, reported in Employment Practices Guide ¶5373.