I'm sure you know this but a good physician will closely track your lung function and on a dip will get a sputum test done and then get you on the right antibiotics asap. That is a very important part of CF treatment that does need regular trips to the clinic. BTW I'm glad you're doing so well :-)
I've had the fortune of being pretty consistent lung function-wise - the dips tended to be when I was doing poorly with my treatment regimen. (Of course there are many who have issues despite their best efforts)