I was the same at that age and personally I think whiskeyron is on the right lines, I hated that time on a Sunday night before school when I had to go to bed, it was dark, everyone else was asleep and I felt alone, it made it even worse that I had to go to school the next day where I felt I had to do well etc.. so it wasn't a case of one thing getting me down, it was when loads of little things such as that come together at once and got on top of me, maybe it could be the same situation for your son.?