Short answer: yes, it's normal...but it does not last and it gets less frequent.
Think of the occasional "funks" as your body winding down from an adrenaline high. You've been jacked up fighting the demon, and occasionally you just get mentally tired of it..just plain worn out. I'll tell you bro, 52 days is longer than I ever did on my own, but if I was you, I'd make day 52 the last day I'd do it alone. Here's just ONE big reason why, and it has to do with how you currently feel: Guys that have posted for 52 days, participated in the forums, and posted a few questions/answers will not be surprised by the funk that you are feeling. They will still feel the funk, but there is no "wtf is this" surprise in it. They will have expected it, and they will have thought about how to handle it. They would know all the techniques to cut through the fog, an they would have prepared for the day when they feel they can't do it any longer. And best of all, when they hit that funk, they will have already burnt the last bridge back to copenhagen. They would have gained all these advantages for the price of a couple of minutes a day.
What I'm saying is this: Why reinvent the wheel? Thousands of these guys have gone through the exact same thing you are going through. They have heard what works, they have seen what fails. Go to the WELCOME CENTER and read about what we do. If you can live by what it means to post roll and understand it's meaning...then jump in.