Seeking an "accomodation" from my workplace HR department

When I wake up in the morning, sometimes I feel weak and a little twitchy in the muscles. And if my eye is a little droopy it is really not safe at that time for me to be driving to work. Thankfully I work in IT and 99% of what I do can be done from home with a good internet connection and a Virtual Machine connection to my workplace.

Since my diagnosis I initially tried during bad days to make it into work regardless but sometimes it was really not safe for me to drive, when the symptoms are bad or when a flare is occuring. So I approached the Director of IT and got unofficial permission to notify him when it was not a good idea and he would allow me to work from home. But he warned that if it happened often enough that he would have to get HR involved and it is happening often enough that it has reached that stage.

HR wants a doctor's letter explaining what is happening to me and that some kind of accomodation is necessary for my health and safety. HR wants details of why I need it so I have to get the doctor to explain MG in general and the symptoms and flares etc. Has anyone else been asked for such a letter. How much detail do they really need.

I am not lazy. I love to work. I am looking for either a scheduled work from home days (Maybe every Tuesday and Thursday) so that I do not have to be exhausted every single day with the effort of getting up, preparing for work, driving to work, and starting the day already tired from that effort. If I have work from home days scattered throughout the work week, it makes the days I do have to go into work a little easier and less consecutive days of draining effort.

Does that make sense? Am I asking for too much?