Although there is a line that can be drawn where an employee can assert a right to medical privacy, there are situations where it may serve the employee's interest to inform the employer about a disability they may have.
Sometimes, employees who suffer physical or mental disabilities need a reasonable accommodation from an employer, in order to enable them to do their jobs. This may include allowing liberal use of time off, depending on the circumstances. But in order for the employer to accommodate the disability they must know about it first. There must be some form of interactive communication to better understand the nature of the disability and what can be do to accommodate the employee to allow them to continue to work. If the employee does not wish to discuss it, the employer cannot be held responsible for its failure to accommodate.
Of course, it is a personal decision each employee must make, to decide what is right for them.
Employer has a right to know, particularly if illness is contagious. They also have a right to demand Drs. letter. You have a right to protect your privacy. You can tell them you have a migraine.
The response given is not intended to create, nor does it create an ongoing duty to respond to questions. The response does not form an attorney-client relationship, nor is it intended to be anything other than the educated opinion of the author. It should not be relied upon as legal advice. The response given is based upon the limited facts provided by the person asking the question. To the extent additional or different facts exist, the response might possibly change.