A question about a 25-year-old boy? My brother is an Asian and studying in university in the United States. For a few weeks, he has been experiencing some nausea and a few spells of dizziness. He's only 25 years old, and we're worried sick about him now. He says that he sleeps well, and has been eating well, too. He doesn't have much physical activity, though, because of the lack of time.
In addition to that, we're experiencing some financial problems with paying his tuition fees, and he has been thinking and worrying about that, too. He's 25 and all his friends have already graduated from college and university. He is holding a part-time security job, working in the late evenings at lonely, construction sites. I think this must be depressing him further.

But, do you know why he's having those nausea and dizzy spells?

Summarized question: What could cause nausea and dizzy spells in a 25-year old man?