Class 1-A was chilling, until the alarm went off:

Alarm. Alarm. This is not a drill. Stay in your homerooms until all clear. Alarm. Alarm

Everyone is panicking now.

Aizawa: GUYS RELAX!

everyone quiets down

Aizawa: There is no shooter! Another student in another class just had a severe medical emergency! You can talk and do whatever! Just stay here until the emergency is over!

everyone relaxes

Bakugo: Tch. The extra who had a medical emergency needs to man up…

Deku: Kacchan! What if the person who had the emergency had something they couldn’t control like an allergic reaction or a seizure?

Iida: Good point, Midoriya.