Inability to do your job for any reason could lead to dismissal. What's important in the process used to investigate your absence as well as the impact it has on the business.
Yes and i've seen the issue have to be raised with someone.
It was initially handled by way of a discussion with the member of staff as to things which might help such as less/shorter working hours, restructuring breaks etc...
Obviously it depends on the job as to the kind of changes which might be feasible.