You suffered from POTS, which is a condition which causes fast heartrate, dizziness and fatigue after a transition in posture, such as standing up.

This caused you to faint. A lot.

The rest of your classmates were informed... well... after they witnessed you pass out for the first time and almost had a heart attack themselves. They understood you weren't in danger if you did pass out and made sure to keep an eye on you when you stood up to ensure that if you fell, they can quickly move to catch you to prevent injury.

Another fainting happened again, while you were getting up. When you came to, you felt a couch beneath you as your eyes adjusted to consciousness. It was then did you see Kokichi's grin, the boy draped over the back of the couch.

"Good morning, sleepyhead!" He exclaimed enthusiastically.