S. J. Perelman

At one point, I didn't get out of bed for, I think, three months, and I went down to the bottom of the hill one day and I had to call somebody to get me to come back up - come pick me up because I couldn't physically walk up the hill.

The historical novelist has to consider what has actually happened, while the SF writer is dealing in possibilities, but they are both in the business of imagining a world unlike our own and yet connected to it.