I went off rather abruptly (unplanned and unexpected) for about 6 days. I did have one night with lower back pain, but it was nothing too terrible. After 6 days, I weighed myself and was up 8 lbs!!!! But dropped those 8 within 3 days. As a bonus, the weight for the next 5 days dropped much more quickly than it had been. I lost an additional 4 lbs. I typically lose 2 lbs a week, so I'm just about where I would have been, if not slightly ahead. I don't necessarily advocate doing what I did. I'm sure it is not good to shock the system like that. And, to be honest, I was an emotional wreck when I saw the 8 lb jump.
The better plan would have been to stay "close" to plan if I couldn't stick to it 100%.