Yes, and if we as a society were more accepting of these types of situational disabilities, workplaces would be much healthier.
edit - Yes, workplaces should cater to legal disabilities. The question here is if employers should in any way cater to functional disabilities, not disabilities as diagnosed in the DSM. See elsewhere in this thread.
Not the person you're replying to, but certainly if you e.g. lose a child, your workplace should be sensitive to that and not fire you because you're unable to show up to work that day.
If they don't want to violate the ADA, yes. For example, major depression can be a disability, and employers are bound by the ADA to not discriminate against people with that disability and to provide them reasonable accommodations.