Answer:
Habituation
Step-by-step explanation:
Habituation occurs whenever people, or even other living organisms are exposed to any repetitive stimuli until the people or the animal, gets desensitized.
Thompson and Spencer, (1966) were able to display 9 criteria that shows whether somebody is having a habituation or not.
But for this question, the example of getting asleep shows a pattern of habituation since the train has to follow a time table, which reinforces the frequency and the desensitization.