People sometimes have impairments that are not obvious, such as Epilepsy,

Under the ADA, an individual with a disability is a person who has a physical or mental impairment that substantially limits one or more major life activities, a record of such an impairment, or is regarded as having such an impairment (Section 2.2).

When a person has a hidden disability, this does not necessarily mean an accommodation is needed. For instance, a sales representative who has a learning disability might have excellent customer service skills and exceed the employer's sales expectation. The EEOC manual also states, "If a job applicant or employee has a hidden disability, it is up to that individual to make the need for an accommodation known" (Section 3.6). However, if the need for accommodation does arise, disability awareness and reasonable medical documentation can help facilitate the process. When the employer and the employee with a disability agree to seek an effective accommodation, making a good faith effort to work together can foster understanding and dispel misperceptions about hidden disabilities.

Information is provided by Crockett Resource Center for Independent Living.