Some questions for clarification:
What version of FM?
How many categories, fixed number or continually adding?
How many fields will need to be displayed/hidden?
If you design different layouts to contain the fields appropriate for each category, you can set up script triggers to move to the layout appropriate for the category concerned.
Or you may want to replace these 10 fields with 1 field in 10 different related records. That then allows you to use your drop down to control the relationship needed to display a different field or group of fields in a portal.
A different option might be to replace your drop down with a tab control with different field(s) on each panel of the tab control so that you simply click a different tab of a tab control in order to access a different field or group of fields.