Answer: anxiety
Step-by-step explanation:
He probably has a fear of travelling in a train or it makes him nervous to travel in a train hence being stressed by this fact he broke into a sweat and became dizzy which are all signs of someone who is suddenly overwhelmed by a seemingly intense stressful situation to them .
The fact that he also feels that the people around him do not seem real is also a sign of being too stressed that you can't even make sense of reality or of what is real and what is not .