First of all, congrats on all you've accomplished! You've come so far already!
That 4 lbs you gained isn't going to be 4 pounds of fat, and won't take you as long to drop as 4 lbs of fat would. So that's good news
I know I have times like you are experiencing, and I'm sure others do too. It's kind of a popular response to stress and change. I actually did the same thing right before hitting onederland, I was sitting at 202 and took a week off and just ate everything in sight. I gained 2 lbs at my weigh-in that week, put my nose back to the grindstone the next week and lost 3. Frankly, I think part of me was resisting entering the 190's. I don't know if you have any latent fear of change/getting smaller but maybe that's a factor - self-sabotage is a sneaky thing.
You know you can pick yourself up and dust yourself off! These things happen, and what's important is that you keep moving forward. Don't let a gain get in your way, it'll be off in no time.