How to help a student researcher with narcolepsy continue research
I have had Narcolepsy for ten years now. I am also currently an undergraduate at university. In my opinion, based on personal experience as a person with narcolepsy, there are a few things important to consider. 


Firstly, the severity of narcolepsy is different for all those who suffer it so abilities vary. I am at university full time and whilst I am offered accommodations to assist me, on the whole, I produce high quality work.
Secondly, a person with narcolepsy may doubt themselves regardless of their abilities because others around them are quick to doubt them. This is why, on most occasions, I have not disclosed my condition to employees. Once I am employed, the quality of my work speaks for itself and then I disclose it for safety reasons. This is an internal battle because I fear that I am being untruthful to start with. At the same time, I know the stigma narcolepsy brings and that given the choice between a candidate with narcolepsy and one without, I would lose. If this person has told you about their narcolepsy it means they trust you and respect you and feel compelled to be completely truthful with you. They probably don't want to let you down so they will probably downplay their abilities in fear of this.
Whilst narcolepsy is characterised by 'sudden uncontrollable bouts of sleepiness', it's usually brief and full alertness is resumed after a short nap. Narcolepsy occurs because the hypocretin/orexin have been fought off by an autoimmune disease. This means sleep/wake cycles aren't regular. A person with their hypocretin intact do all their sleeping in one block, usually when the sun goes down. A person with narcolepsy sleeps in smaller blocks of time and stays alert for a shorter amount of time. Theoretically then, a person with narcolepsy can be awake and alert for the same number of hours a day as a non-narcoleptic but needs to do this by by breaking it up into smaller blocks. (You could liken this to differences in diet - some people eat three big meals a day while some people eat six smaller meals a day.)


To conclude, yes narcolepsy makes my life more difficult. I wouldn't be able to succeed at university without the support and understanding I get from the staff. But life is full of challenges and it is the way in which we deal with them that sets us apart. If you have developed a good working relationship with this person, then they already fulfil one important aspect of those needed for the position. A person with narcolepsy is aware of their shortfalls and given the chance, will do what is needed to overcome them. Don't let a diagnosis change your perception - just because a person doesn't have a medical label attached to them, doesn't mean they don't have other relevant faults or issues.

My advice is to write down what is required to fulfil the needs of the research - do it in measurable terms. For example., how many hours a day/week is sufficient? Then sit down with this person and discuss it with them. Approach the requirements as you would anyone else. (For eg. Can you commit to these requirements? etc) If you were happy with their work previously tell them that. Also admit that you don't know much about narcolepsy but you know that everyone is different. Tell them you want them to succeed and you have faith in them. Tell them how important the work is to you and if you think you are a good team, say so. 

I hope this has been helpful and thank you for not listening to your human resource department who clearly lack knowledge and empathy.