I am in the process of writing my bachelor thesis, but my mental health has been in very bad shape lately, although I'm starting treatment soon. I am confident that it already had an effect on my productivity, and I can see the treatment procedure also affecting my productivity in the future. It was therefore advised to me by the "student advisor" (a member of my faculty that advises students about general concerns) to let my thesis supervisor know about my problem.

However, I am not sure how to go about doing this in regard to how specific I should be in describing my issues. One possible option would be to let him know that I have some sort of mental health issue. The benefit of this would be that he might be somewhat more receptive and understanding of my decreased productivity (and possible other problems). On the other hand I'm afraid it might be a bit harsh on him, because he might me reluctant to mark my thesis as insufficient or to have tons of negative commentary. (realistically speaking, I'm sure everyone involved in grading my thesis will understand that me not passing will not affect my health positively, to say the least) How should I approach this problem?