One of the first aspects of meditation is training the mind to be able to concentrate or focus. Without that the mind drifts or gets bored which leads a person to doze off or sleep. Concentration and focus are challenging because we are used to a great deal of stimulation in our day-to-day lives. If you watch TV or movies notice how quickly there are edits, changing camera angles and positions, and having the camera in motion. This is quite intentional because most people have a very short attention span of only a few seconds. So movies and TV cater to that and the movies and TV in turn reinforce short attention span in people.