There are many times I am thankful for being a Gemini. It enables me to switch hats so quickly others might get whiplash. Going between past and future when I write and having to spend several hours of the day in the "real world" is enough to make even me dizzy sometimes, but now...
Now I am in the midst of writing two different series with various characters which cross between them, one series set predominantly in the past, the other predominantly in the future. The problem? I am writing them both in the first person. This means having to stay inside the head of one of them during one series and the other during the second series and never letting either character know something he shouldn't or have experiences outside his own realm of knowledge. This also means making sure the voice is right for each, the reactions, the emotional make up, and the psychology.
It is easy in "The Glastonbury Chronicles" to go back and forth between the King and the Knight, by whatever names they have in those lives (and by whatever faces they wear) as they become more and more telepathic with each other as the books progress. They are bound to have similar voices and similar psychologies, as they have been bound together for millennia. Yet there comes a time where even they diverge, and finding there are certain secrets they do have from each other, certain corners of their hearts which can express their individuality in ways the other does not always understand came as a bit of a shock to me.
But then, I have always maintained I do not write these books, I am merely taking dictation from characters who somehow seem to have lives of their own.