Creating a form with a internal database

Super New Learner back again with another super specific ask.

I am starting from the drawing board with a really detailed form for my company. I have now purchased Pro for myself and trying to get this to work. 
I am looking for a way to implement a Database into the Documents Javascripts where all the dependant drop downs (in the hundreds) could make selections that change dependant dropdowns and so on.  I have tired coding it into each box but it slows down the documents ability to show the selection as well as change the other dependant boxes.
Here's an example of what I am doing. One box selects the Subject from a list. That Subject then pulls multiple choice answers for Dropdown1 which dictates the selections that can be chosen for Dropdown2. (Complicated I know) 
I was originally trying this with the SetFieldValues Approach but having a hard time getting an handle on what I need.

Example of what I am looking for:

List of Subjects Dropdown: Diagnosis1, Diagnosis2

• Selection of Subject dictates Dropdown List of Methods specific to that Subject: Exercise, Surgery,  Discharge
  • Selection of Method dictates Dropdown List of Options specific to that Method: Schedule, Defer, review, Follow up

While I was using SetFieldValues, Switch Event and ever other simple way of trying to get this done I'll admit I am just a little over my head...again. I fear that I am not using the correct verbiage to get my point across in my own research efforts. Can anyone advise or point me in the write direction?  Any help would be greatly appericated.