Mainly it's because a lot of memories come flooding back to me from the past that trigger me. It could be caused by a conversation with a teacher, and then me going away and over analysing and obsessing over that conversation. I get anxious pretty much every day, about a lot of trivial things - the most common is when I get to college and I get anxious over whether I'm going to the right lesson, even though I have my timetable right in front of me.

I'm exactly the same as you! I either overeat in the evening, or I don't eat anything for a few days.