I lived overseas for a time in an area that didn't use English. I loved it, enjoyed being there, but one day I noticed that I was talking to myself! At first, it was just exclamations out loud (quietly) when something happened around me. It progressed to me describing or evaluating my meal, a book, a scene I was looking at. I realized it when I noticed ppl looking at me strangely (they normally did anyway), and as I looked back wondering why they were looking at me, it hit! I had been talking out loud to myself, normal volume! Why? I figure it was loneliness; but loneliness for hearing English. I was the only one who could speak it! And then it hit me again, a new found epiphany about all those "crazy homeless" ppl who I'd seen back home, muttering to themselves as they wander around. What if, instead of (or in addition to) being mentally unwell, they were just lonely, and having no one to talk to led to them talking to themselves? Whoa.