"We bumped into him in the hospital. He looked upset."
I was pretty sure the subject and location are able to be switched, like 在医院我们遇到他。Is this unnatural or something?
It is acceptable. However whether it is natural or not depends on additional context. Word order does change the focus and perspective of a sentence. We can ignore the effect first until a more advanced level, but it is needed to acknowledge that they are not really perfect equivalents.
I don't think you can do that with a location prepositional phrase in Chinese, but I'm not 100% sure, though.
It is necessary to have a magnitude. It can be 很 or other magnitude indication.
I really just wish they were consistent with the 很. If you want me to use it, put in a very.
I am a bit confused about word usage here - I find that upset and angry are close in meaning and upset and sad are not close in meaning - but DL seems to equate upset and sad with 难过。Can a native speaker clarify?