It's crazy you just posted this. I had the exact same thing happen to me yesterday with the same weight except on military press. I did 200x5x5 easily last week but could only get 3 reps on my first set with 205. I thought for sure I would be able to get 5 reps for at least the first few sets. I feel your frustration. When you work really hard at something and don't see results it inevitably makes you feel terrible.
But if there's one thing I've learned about lifting it's that persistence is the most important thing. EVERYONE has bad workouts. No one can accurately predict how they are going to perform every time they lift. The people who get strong are the ones that keep getting up after their failures and never, never quit.
If it's any consolation I was going to just deload down and do high rep sets for awhile 15-20 to take pressure off my joints. I figure once I get back to the heavier weights I'll be more prepared to handle them. I've not had much luck using 5x5 at all. My body seems to respond better when I just do 2-3 sets with maximum ball-busting effort. Maybe something similar will work for you? I know people are going to disagree with me but I think you have room to get stronger at a quicker pace before you start a slower gaining program like 5/3/1.