Why did she all of a sudden stop texting? What should I do?

Well I think that you should just send her a casual text asking if everything is ok otherwise it will seem as if you don't care about her at all. If she doesn't reply or is still off then it would be a good idea to give her space. :-)

I'm quite close to this girl - we text each other a fair bit, almost everyday in fact, the majority of which she initiates.

Anyway, for the last four or five days, she seems very offish. She hasn't texted and I haven't as well. On top of that, in lecture yesterday I went past her (which she knew) but she didn't even look at me.

I'm puzzled as there was nothing to suggest this distance would develop. What should I do?

- Should I text her? She may not want to talk to me though.
- Or should I just leave her alone?

But I didnt do anything wrong to her. But I think your idea is good.

Lol! Yeah you might not have done anything but it would show that you noticed and it would not do any harm to send a text or even speak to her about about something that IS bothering her. She might not tell you but sometimes the gesture is more than enough. :-)