I've been running 10K for my long distance runs (yes, I consider 10K long distance, because I refuse to do cardio for more than an hour; it's all about them gainz). I used to join those monthly 10K fun runs, and my average time till last year was sub 1 hour (55-58 minutes). This year, I've been clocking in beyond an hour at the finish line. I notice that I usually slow down at the 7K mark. I've tried various training programs online, or even on Nike+ coach. I just couldn't break the 1 hour barrier anymore for 10K. I'm not sure if age is starting to show (I'm 37), or lack of sleep since I just became a dad. To give a better illustration, my last sub 1 hour 10K run was back in March, became a dad in May, and started running again in June. My last 2 10K runs were both 1 hour and 8 minutes. Back then, I'd stop running for 2 months, come back, and would still clock in sub 1 hour at the finish line. Is it normal to slow down overnight?