It didn't happen to me, but now I know am right to be worried about it!
Several years ago now, when riding on a super-crowded rush hour subway train in Tokyo (one of those ones where the station workers push people into the train), I had a panic attack when I suddenly wondered what would happen if the train stopped for some reason and we were stuck in the train for awhile. I had to get off at the next stop, and since then I do anything to avoid those kinds of rush hour trains. These days, if I have to go to Shinjuku station in the morning, I take the bus--it's a 35 to 50 minute ride, in contrast to the 10 minute train ride, but I don't panic!
Anyway, on tonight's news, they reported that a crowded rush hour train stopped between stations due to some kind of problem. People were stuck in there for two hours before someone came to lead them out. It was in one of the newest subway lines, the Oedo line; because it's new, it's very deep underground (so it can run under all the other lines). I always feel nervous when I take that line because it's so far underground. Anyway, because it's so far underground, the ventilation is not very good--50 people fainted or had to lie down while waiting to be rescued, and 10 were taken to the hospital.
Anyway, now I feel that I am definitely right to avoid those trains!
Luckily, when I go to Waseda, I can take a train that isn't very crowded. I have to walk 25 minutes to the station (or else I can take a bus if I am in a hurry), but I can sit down on the train for the 10 minute ride.