Adventurous way to use excel. Apart from the large RAM requirement to run the query, it would be a pig to administer. So, unless you have a definite reason for doing it this way, I’d use a db in the following way.
I think I would have created an Access db with the symptom in one column and the treatment in another, then after the user indicates that they have entered all the symptoms I’d do a filtered search on each symptom retrieving the treatment, into the adjacent cell.
As an added refinement, I’d do a sort on the treatment column, (that way all the same treatments could be together,) then a copy unique sort could be done to shorten the list of treatments presented to the user.
Just an idea. Good luck.