It sounds protruding , but I think they are talking about health and safety . These days employers are getting more vigilant than the old days ,and to get it in writing means it is official . At least you are happy with your job , don’t worry about anything .

By asking they have shown their concern for you and more importantly for them i assume it meets there HR requirements incase you harm yourself in any way while at work they have a paper trail and you cant sue them :p
Hope ur feeling better and got stuff sorted with ur week off… x

stories are great to read

Did they give any explanation as to why it was needed.

I am not 100% sure, but maybe they asked for it just to cover their own back. I would try not to be too upset and think of it more as they are following procedure.