In "The Metamorphosis" by Franz Kafka When Gregor is trying to get out of bed, he considers calling for help but then dismisses the idea. Why?
Gregor does consider calling for help, especially after he spends more than twenty minutes trying to get out of bed in his new, insect form. He thinks,
Well, leaving out the fact that all the doors were locked, should he really call for help? In spite of all his miseries, he could not repress a smile at this thought.
He knows, of course, that his family would be utterly shocked to find him in the condition in which he finds himself. Around 6:45 a.m., Gregor's mother had knocked at his door, asking if he was still planning to catch the train to work, as normally he's up hours before this time, and he realizes that
their little exchange had made the rest of the family aware that, contrary to expectations, Gregor was still in the house, and already his father was knocking on one of the side doors [...]. At the other side door, his sister moaned gently [...].
Gregor's family is apparently so used to their routine that they are now too rigid to meet any change in that routine without a great deal of anxiety and concern. If they are so alarmed by the simple fact that Gregor is running late, imagine how they would respond to learn that their son and brother has turned into a giant bug? The thought of their reaction does seem to make Gregor smile, but, ultimately, he cares for them and would likely not inflict such pain on them if he can help it.
Another reason Gregor dismisses the idea of calling for help is that he is embarrassed and unnerved by his present condition. If we look at the text, we can see that Gregor is used to being an independent, capable, and industrious man. That is simply the way he operates in his daily life. After all, he is the main provider for his entire family.
Now that he has turned into a giant insect, Gregor must take stock of his situation before he faces the world. He must ascertain whether his present condition is "purely imaginary" or a permanent state of affairs. Thus, the act of getting out of bed (however difficult) must be attempted. In order to figure out a solution to his current crisis, Gregor feels that he must not relinquish his long relied upon self-sufficiency. His desire to be autonomous (despite his current, unexplained handicap) is an attempt to hold on to his sanity. This is why he doesn't ask for help, despite the temptation to do so.
According to the text, Gregor has already determined that staying in bed is not an option. He knows that he cannot reach a "reasonable conclusion" while sequestered helplessly in bed. Since he also doesn't want to alarm his family unnecessarily, Gregor decides that he must make every effort to get up by his own power.
What is striking about the first chapter of this novella is that Gregor wakes up one morning to realize that he is changed into a "monstrous vermin" and yet he doesn't seem all that bothered by the fact. He is frustrated over his inability to get used to his new body, but he never asks himself how this happened, why it happened, or what he could do to return to his normal self. There is no textual answer to your question, but you need to infer from his initial reaction and lack thereof that Gregor thinks that he is merely changed for the moment and that he will return to normal soon enough, and in the meantime he doesn't want to alarm anyone. He seems to think that if he can just get out of bed he can get himself together enough to go to work like normal, even if he will be a little late. Gregor is also extremely sensitive to the sensibilities of his family members and he doesn't want to alarm anyone else with his changed self. He sacrifices himself in large and small ways to please his family, and this choice to not ask for help is just another example of that behavior.