How do I avoid or get past the post-orals slump?
The most urgent thing to do is to take a short vacation and celebrate. Go do something fun, unrelated to your research. If you live near a beach and the weather is nice, sit on the beach with a non-technical book. Go to any local tourist attraction. Eat a nice dinner with friends. Watch a movie. 

A few days delay will not cost much, but could bring enormous benefits in your readiness to get on with the next steps.