is it correct to say that the sentence
"the guy has been overwhelmed by his boss"
"the boss is so demanding and is putting so much pressure on the guy that this one is not felling well and comfortable with the situation"
It could have that meaning, but it could be a bit too specific. Certainly, the boss has had a very strong effect on the employee and it has affected him a lot, but it doesn't necessarily imply pressure- it could just be the strength of the boss's personality.