A number of California cases hold that simply notifying the employer that you are sick and cannot make it to work for a day or two does not place the employer on notice of disability and thus does not trigger ADA protection at workplace. In Avila v. Continental Airlines (2008), Plaintiff submitted a number of Kaiser forms related to being absent from work for several days. The forms stated that the employee is excused from going to work for one or two days. The same forms did not provide any information about the nature of the employee's condition or the diagnosis. Thus, no disability discrimination claim could have been brought against the employer, since the employer was simply not aware of any disability, even though the employee suffered from pancreatitis, which is a serious condition that by all means qualifies as a protected disability under ADA.
The lesson that can be learned from the above case for the employees is that the employee should ensure that the employer is aware of the specific condition that the employee is suffering from or the basic symptoms that clearly indicate that it's not just trivial illness such as a flu. When obtaining medical note from the hospital, it's a good idea to ensure that the documentation transmitted contains sufficient information about the employee's condition, and is not limited to just for how long the employee is allowed to be absent from work.