I have been blessed with a wonderfully flexible job. A couple months ago when I got so sick I was thinking of going on disability and no longer working, but I'm happy to report I'm going back to work part-time next week. I also work part-time as a professional freelance writer.
Working, managing health and having a home life/social life is indeed a delicate balancing act. I've learned that by putting health first, the other aspects of my life fall into place more easily. I've learned that I cannot "borrow" energy against tomorrow. I have to carefully consider what I do in a given day and be very wise about how I spend my time.
It's a challenge to work full time and manage CF, but it is doable. That being said, not everyone can handle it. If you're one of those people who simply can't make it all work, there's no shame in that.