The first set of dehumanizing circumstances swim through Gregor's mind as he's trying to sort through what has happened to him: he needs to go to work, and to do so to pay off his parents' debts. There are many theorists who argue that capitalist labor is innately alienating—it's a major tenet of Marxism—and even if it is not, it would have to be depressing to have to work for someone else's debts, not your own. This is underscored by how the clerk treats Gregor when he visits: Gregor is only a job-filling thing to the clerk, not a person. He cares about the work getting done, not Gregor as a person. That's dehumanizing.
Interesting question! In the story The Metamorphosis by Franz Kafka, Gregor feels dehumanized even before his transformation from human to bug! This is especially evident in his reaction to his transformation.
At the beginning of the story, Gregor realizes his transformation. Instead of responding with fear or astonishment, Gregor focuses primarily on his work. For example, as Gregor's thoughts reveal:
“what a demanding job I’ve chosen! Day in, day out on the road. The stresses of trade are much greater than the work going on at head office, and, in addition to that, I have to deal with the problems of traveling, the worries about train connections, irregular bad food, temporary and constantly changing human relationships which never come from the heart.”
Furthermore, Gregor fails to realize that something is wrong with him. As Gregor thinks about being late for his work, he considers calling in sick. However, he fears that his boss would have a doctor check on him and that the doctor would indicate that Gregor is simply making excuses. As the text illustrates:
“The boss would certainly come with the doctor from the health insurance company and would reproach his parents for their lazy son and cut short all objections with the insurance doctor’s comments; for him everyone was completely healthy but really lazy about work. And besides, would the doctor in this case be totally wrong? Apart from a really excessive drowsiness after the long sleep, Gregor in fact felt quite well and even had a really strong appetite.”
Thus, Gregor’s reaction to his transformation illustrates that he already feels dehumanized. Although Gregor is aware of his physical transformation, he still believes that he must continue working and that he is capable of doing so. His excessive focus on work and the pressure from his boss, family, and even himself cause Gregor to feel less human, even before becoming a bug.