If there is inflammation, trauma, or neurological disorder in any one of the six muscles which control the rotation of the eyeblaas, then the actions of the optic muscles will become very discordant, thus limiting the rotation of the eyes, and the images of the object seen by the two eyes can not locate in the same spot on the retina, which makes people see two same objects, making the double vision. There are some reasons to cause double vision, such as impotence or paralysis of the extraocular muscles, disturbance in the cranial nerves, strabismus when reading. In your case, it can be strabismus that make you get double vision, that is, you do not use your eyes in a correct way when you are reading. For example, you have habits of reading while lying in bed or placing your head on arms, making the optic muscles transformed. Therefore, you should get rid of these bad reading habits, and go to the doctor's for an eye examination, and usually the doctor will ask you to wear eyeglasses to help correct your vision.
Your double vision after reading your novel may be caused by the tiredness of your eyes. You must have read for a long time with little rest. Your eyes nerves will be tired. You should have the good rest for the eyes. Then you need to use some eye drops to moisture the eyes and release the symptom of double vision. You could also use the warm compress to make your eyes get comfortable.
In your case, the double vision may be caused by excessive concentration on the book. When your two eyes cannot work coordinately, double vision or diplopia may happen to you. Normally, your eyes will point at one object at the same time and the two images saw by them will be synthesized into a single image. However, when your brain cannot process the two images into one, you will experience double vision. Double vision is more likely to occur in long time of reading or concentration on near object. Strabismus, head trauma and presbyopia are also the causes of double vision. If you start to have double vision recently, you should have your eyes examined, for a sudden double vision can be the sign of brain pathology. Eye dryness can lead to double vision. So, try eye drops to lubricate your eyes and the double vision may disappear.