To add drama and plot to the upcoming episodes........
And also because he was not right in the head (seeing Lori, talking to dead people on the phone, etc.). Has he snapped back after that trip to visit Morgan?
I don't think that this is a very good answer. As viewers, we understand that it's not real and that there is an actor who plays Rick and the Governor and everyone else. But we suspend that disbelief in order to enjoy the show. Yes, the writers write things for their own purpose and to move the show along, but as viewers, we sort of expect things on the show to make sense because of things on the show, not because it makes sense in the writers' world.
These last three episodes are a good example of this. AMC ordered 13 episodes for Season 3, but upped it to 16 because of good ratings. The writers already knew what they wanted to do in their 13 episodes, but now there were an extra three episodes to fill. So we got three bottle episodes that didn't move the story at all. The first, with Morgan, happened to be very good. The last two were pretty bad. I understand why it happened. I understand how it happened. But that doesn't mean I don't want stuff on the show itself to make sense, just because it is convenient for the writers.