Ok, so a familiar pattern seems to be emerging: For the first part of the year, up until my holiday, which is usually end of July (last three years mountain biking in Canada), I ride my bike alot: Road riding during the week and mountain biking at the weekend, and never get ill. I then have my holiday, and spend August doing a mixture of riding bikes and celebrating my birthday. Then, come September, my body seems to shut down and I become the target of every bug going.

This then appears to last until after Christmas, at which point I seem to be able to slowly get back to full fitness again.

Anyone else experience anything like this?