It's not as simple as whether the termination is because he is disabled or not. An employer's obligation to make "reasonable accommodations" to a disabled employee, which means changes in how the job is done, or the provision of some assistive devices, which are not too expensive or too disruptive for the employer. However, an employer is not required to run an enhanced risk of liability, such as from an employee who collapses at work (and so could then potentially try to claim vs. the employer, or who, while collapsing, could damage equipment or injure another), nor are they required to retain an employee who, even with "reasonable accommodations," is not productive or can't do his job. From what you write, the employer may have been worried about liability from your husband collapsing. It may be that their concern was overblown and unjustified, and therefore that this is disability-related discrimination...but it's not  automatically the case that it was, because employers definitely may let go employees who have conditions making them prone to collapse in many circumstances. It would be worthwhile for you and your husband to discuss the matter in detail with an employment law attorney; you just need to be prepared that this termination may be justified.