Slumps can and do happen, and they happen to everyone. Even the best players in the world do not bowl well every single time they step out onto the lane surface, so don't have a breakdown just yet. There are a couple things you should look at though on the physical side:
1. Have you been keeping the surface on your equipment? Bowling balls can
Track out, especially these new hook in a box ones. They can lose their punch on the back end of the lane, and this can cause weak 10's where there used to be strikes.
2. Has the lane conditions changed? Even though house patterns are generally easy, changes in weather and humidity can and will change the way bowling balls react. If you are dead set on one specific way to bowl in your house, these changes can effect you tremendously. Don't be afraid to move.
As far as the mental side goes, it's just something you have a get through. 300 is just a number, and should not translate into the skill of the player. a guy with 10 300 games is not necessarily better than a player with 2. I've seen guys with 15-20 perfect games that were just terrible once you took them out of house conditions, so don't let "300" make you crazy.