Employers are required to reasonably accommodate people based on disabilities and medical conditions. What is reasonable is up to debate. It would also require that you can show they fired you for that issue, which can be tricky because they can always find some legitimate reason to cover their true motives.

One example of this could be an alcoholic. Maybe they showed up to work drunk. If they tell their employer that they are an alcoholic, the employer has to offer to get them help before they can fire them. If they refuse help or the issues continue, then you're allowed to fire them. Now if they never told the employer about their condition, the employer could just fire them because maybe it was just a bad decision to stay out partying all night, which is not a medical condition.