For the first two months or so of the summer, my training was going fine. After track season I took a little time off and then during June ran 18.5 (4 days), 22.8 (4 days), 30.2 (5), and 33.6 (5). In July I ran 41.5 (6), 40 (6), 44 (6), and 44 (6). During the last two weeks of July I built up to a long run of about 9-10 miles. In addition to running I've been doing a little bit of biking and swimming as well as lifting upper-body weights 2-3 times a week.
I've been doing most of my runs between 7-7:15 pace, sometimes a little faster. I started doing a weekly tempo or fartlek in the 2nd week of July, and then last week I did both. Starting very suddenly on Saturday (my day off that week was Friday) I felt very tired and was running much slower than I felt like I was. I felt the same way on Sunday (during my long run), and so I decided to take the last 3 days off (both to help recover and because I was traveling and was tired from standing around airports waiting for delayed and cancelled flights and didn't have much time to run anyways). Today I ran about 5 miles close to 8:00 pace and I nearly collapsed after finishing it. The only way I can describe how it felt is that it seemed like I was running up-hill for the entire run; I had to fight to make every single step. This came very suddenly and I'm wondering if anybody has any idea why I'm feeling this way or how I can stop it.
SPARKNOTES: Last Saturday I started feeling really crappy while running and I couldn't run anywhere near as fast as I usually do. I felt the same way Sunday, so I took off Mon-Wed and felt even worse today.