Luck doesn't really come into play to achieve the top results. I do understand the difficulty if you have been achieving at the top of your school for the past few years and it is easy to burn out. I could strongly suggest that you ignore everyone else and focus on yourself. You are competing against yourself, improving against yourself, competing with other people will simply be an endless pursuit that is meaningless. Consistency is the key to achieving good HSC results, it was the one word that got me throughout the year, you have to try your absolute best to achieve consistent result. If you have any future speaking tasks, please feel free to check out my thread on how you can ace your oral presentations
http://community.boredofstudies.org/4/english/318818/how-ace-oral-presentations.html
I did experience a big jump and drop, I remembered in year 11 I got less than 50% for my first Maths Extension One task, you can imagine how 'down' I felt, however, I used it as a motivation to keep going and eventually ranked second internally. I remembered in year 12, because of performing extremely poorly for a chemistry practical task, I was basically in the bottom half of the cohort, but because my results for the other assessment tasks were quite good, it reduced the impact of that assessment task on my overall internal rank. Consistent results are hard to achieve in year 12-but that actually goes for any year you are in. I would strongly recommend you to set yourself consistent goals in terms of results you wish to achieve and try your best to achieve them, and compete only against yourself, never against others
Remember, learn to define your own results, never let your results define you
I wish you all the best for the rest of this year, if you have any more questions, feel free to ask on this thread