My long runs are once a week, and I run at about a ten minute mile pace when running more than ten miles like that. Other days (4 days during the week) I generally run 3-5 miles depending on the day at a much faster pace. The general malaise and fatigue came later - basically I did a 12 miler on a saturday, started low carbing it that day, and from that saturday to the next friday was when I was feeling shitty and fatigued.
Now, a few caveats: 1. I ate a lot more calories that week compared to the week before, because I knew my body would not be able to sustain low cal + low carb and do all the cardio I've been doing. 2. Feeling better now, but I have been eating a *few* more carbs this week generally, although still been doing all right. It's just that I have had a few moments of failure - ate one donut yesterday, two cookies on sunday, etc. But no big binges or anything. (max of 100g of carbs on two days, 50ish or less on all other days since last sunday). So I'm not sure if the feeling better and more energetic is due to sneaking more carbs in this week, body adjusting, or some combo of both. Since I'm going to go totally undisciplined this weekend (big get together, don't ask), I'm not doing too well being scientific about this whole thing, but starting monday I will be back on it, and hardcore.