Hi Laura,
I am also 20, however I did start uni and do freshers before at Leeds. (unfortunately wrong course choice) So I am going to Northumbria this September too.
Freshers was really good before, you do as much or as little as you want. Its simply the first week before your course starts to get settled in, get to mingle and have fun. Before all the work starts. I'd say its pretty useful. Not every one goes mad you will find people who are like you too. They organise all sorts of events/nights/gigs, you can join societies .. if I remember right domino's pizza gave away free pizza slices at leeds when I was there. Haha well students will keep their costs down by eating free food.
My partner is also going to Northumbria and we have some how ended up in the same halls, that's going to be a unique sort of situation. But its going to be fun no matter how you spend it.
I am doing motion graphics and animation. And will be in new bridge street accommodation.