It's a marathon, not a sprint! lol Just had to get that in there.
I just skipped a day yesterday myself. I've a had a bit of a cold and it's been bothering my asthma, I had been trying to push through it for a few days, but just gave in. Once I decided to just rest, I couldn't believe the level of fatigue that set in. I don't even know how many hours I ended up sleeping yesterday.
And I can tell you how much better I feel today, though I'm not going to kill myself today in the gym since I'm still not 100%. Exercise is a stressor to the body and so is illness. You keep pushing throughout it, you just end up getting really sick and missing lots of days. I was finishing up school last fall and did just that. I ended up with the worst case of bronchitis I had in ages and was barely able to breathe, much less exercise, for weeks.
You sound very committed, not an excuse-maker. Trust your gut and listen to your body. We often forget how many amazing changes take place during rest. If you keep pushing, your body has no time to repair and you are actually sabotaging your efforts. One day off, just like one day of poor food choices, every once in awhile is not going to ruin your progress.