Does the Hadith, "O son of Adam, if you are not content with what I have allotted to you, I shall unleash the world upon you, and you will chase after it..." apply to a young man who left teaching in his country and traveled to Saudi Arabia to improve his livelihood, and is the hardship he experiences due to his rebellion against his previous life and sustenance?

There is no objection to traveling in search of sustenance as long as it does not entail a religious prohibition, such as neglecting children, being absent from one's wife without her consent, or committing a sin. Traveling for work alone is not a cause for insomnia and distress; rather, contentment with what Allah has ordained brings tranquility. One should increase in worship and remembrance of Allah to remove distress.