In line with Health & Safety obligations and the Equality Act 2010 it is the duty of every employer to consider any health issues that might affect an employee's ability to safely fulfil their job. This is to ensure that consideration can be given to any adjustments (section 20 of the Equality Act 2010) or adaptations that might be required in respect of working activities, hours, shifts, absence, breaks etc. The company is required by law (Health & Safety legislation and the Equality Act) to consider this information as a duty of care to its employees.
Every sufferer will be different when it comes to reasonable adjustments and the job they do, this should be discussed on a regular basis, and what can be achieved within the workplace. Please bear in mind that not every adjustment can be made to Cluster Headache sufferer, this will always be based on the resources that the employer has available to them
With regards to your absence, then any absences as a result of you CH can be recorded separately from any others as CH is a disability. See about getting the companies disability policy if they have one.
If you have any issues or questions please contact Jason on firstname.lastname@example.org.