Nah....

BEGIN 
   FOR indx IN 5 .. 1 
   LOOP 
      DBMS_OUTPUT.put_line (indx); 
   END LOOP; 
END;

Use the REVERSE Keyword

BEGIN 
   FOR indx IN REVERSE 1 .. 5 
   LOOP 
      DBMS_OUTPUT.put_line (indx); 
   END LOOP; 
END;

Or You Could Get Ridiculously "Fancy"

BEGIN 
   FOR indx IN (    SELECT LEVEL 
                      FROM DUAL 
                CONNECT BY LEVEL < 6 
                  ORDER BY LEVEL DESC) 
   LOOP 
      DBMS_OUTPUT.put_line (indx.LEVEL); 
   END LOOP; 
END;