The Web of the Worlds — Harry Harrison

“This must be another world altogether, separate from his own in time and space. He wasn't sure about the details―it had been a long time since he had read H. P. Lovecraft―but this theory seemed the most tenable.”
Grant O'Reilly was not the adventurous type. A sheltered invalid as a child, who used books for accompaniment, he had barely begun to live his life before the great change occurred. Suddenly, about to be married, he is taken by a seizure to wake in a land like none he had known before. Plucked by accident by the fates, he is carried away to a medieval world of wintry weather and barbaric battles. Berl-Cats, fire salamanders and Al'kahar ghouls, existed in this world. He will have to toughen to this strange, brutal world -- or die in it!