It could be, OrmIrian, or it could just be that you've overdone things a bit with the training and your bosy is telling you to back off a bit. Not sure what level you've been training at but sometimes after a period of feeling great and doing really well, you hit a bit of a low and every run is a major effort. Could also be the ibuprofen you've been taking.
I'm afraid I'm not such an inspiration any more as I have decided not to do the marathon. The heavy cold I had a couple of weeks ago turned into a nasty, chesty cough and I was forced to abandon running for over a week, as I felt so awful. I then attempted to get back into the schedule with a 20-miler, but by halfway I was utterly exhausted and had to turn for home early, completing 16 out of the planned 20 miles. Then I got a minor stomach bug, and came to the realisation that I've just been pushing myself too hard and was completely run down.
I had a long, hard think about things and reached the decision that my priorities are different than they were when I ran my marathon PB in 2006. I have a baby son and he's my number one priority. I also work part time (three days a week) which involves an hour plus travelling each way, plus I need to give some time to my hubby and have some for myself. I had stopped enjoying running, finding it just another chore to be crammed into an already hectic schedule. there's no point doing something you're supposed to enjoy if it's making you miserable (not to mention unwell) so I decided to can the marathon. I felt so relieved once I'd made the decision, and now I can run for enjoyment rather than because the schedule says so.
For the time being I'm cutting down to 3x a week as hubby is very busy at work and is having to stay late quite often, which means I can't get out. He's happy to commit to leaving on time once a week though, so I can get out, as well as his Wednesdays at home when I also run because I don't have to wait for him to get home. So I'll probably do a run of 10-12 miles at the weekend, and then two of between 5 and 7 miles during the week. Hopefully this will be enough to maintain my current fitness and speed. I'm actually looking forward to freeing up a little more time in the evenings, especially now we're heading into better weather (hopefully) and lighter days. So, onwards and upwards!