One day one of my classes was moved 30 minute earlier than usual, and I walked in and they were 30 minutes into class and I froze. I kept figeting forward thinking "I guess I go sit down." And then fidgeting back, "But does this mean it is my class or a previous class and I shouldn't barge in." So I was shaking like a fibrillating heart for like 3 minutes until the teacher explained what was going on.