I understand entirely where you are coming from!
The main thing, as OzKo stated, is that there is a lot of social pressure surrounding the HSC, even though in all reality, none of the courses' workloads are terribly difficult or unmanageable. What makes it difficult is all the family and friends dropping by with very exaggerated "oh how is it going?" and "just get through it all" and "it's nearly over finally" and all the media reports playing it up to be some hyper-stressful inconceivable year/moment in our lives, which makes it seem like it's been a draggy year full of impossible work and ridiculously poor time management which naturally stresses you out. If you are smart you really have nothing to worry about and just do the HSC at your own pace - it's probably faster than how school is going anyway. Try to separate yourself from everyone else who stresses unnecessarily much because they never help, and just embrace a little bit of independence now. I found that it helped me to deal with stress when I learnt on my own, or at least distanced myself from everyone else's stresses about not getting into med and then having to become a hobo because they didn't get 99.95.
And to answer your question, it'll depend entirely on you. If you are a naturally independent person then university won't be too stressful at all as you are given academic independence. It is laid back in the sense that lecturers and tutors don't chase you up on your progress with homework and assignments - it is entirely your own responsibility. I hear with a lot of Arts degrees (my girlfriend is currently doing a Communications (Writing and Cultural Studies) course at UTS and just generally friends doing Arts at other unis) that there is a lot of essay writing and reading, which I guess can be stressful, particularly if you're not passionate about learning linguistic theory, cultural theory, etc. I'm currently doing a B Business/Laws degree at UTS, and it's only early into my Law degree so I cannot really make a comment on it and everyone just says it's hard because it's Law without giving any other reason than "there's a lot of reading and memorising". But what I've learnt regarding people who harp on about how hard courses are, it's generally mostly because they have poor time management skills themselves and didn't apply themselves properly based purely on the reputation of the subject being hard.
I think in general a lot of stress comes from the self-fulfilling prophecy of things having a reputation of being hard/stressful. If you separate your mind from the reputation and just apply yourself, you'll feel more comfortable and relax a bit. It's something I've tried to do, and I can tell you now that even though I can recognise that uni is faster and harder than HSC, I'm enjoying it more, getting better results, and hardly stressing at all about coursework and exams.
