Welcome here, while I'm not sure of the significance of your name but I do recognize Apollo 9 which was a symbol of complete success when venturing into unknown territory.
To watch your ATAR going down and not being able to sit down and work is very frustrating -and worrying, particularly as you are unsure of the cause. Academic performance seems so important it tends to overrule other things like stress reduction and a balanced life..
You mentioned this procrastination even apples to things you might enjoy, such as gaming or hanging out.
Different from mine, which only applies to things that I have been worried about and is due to anxiety conditions (study for tests - yes, seeing freinds - no).
When you said you had been brought up in a particular way did you have something specific in mind?
I do not know a great deal about ADHD except I believe it promotes concentration problems. May I ask if you have seen your doctor about this? Just wondering about causes is a worry in itself, if you can find out why there may be ways of getting around the problem.
In the interim is there someone who can sit down with you and help you with your studies?
I wold like it if you came back and talked some more
I too have procrastination problem, but know it's cause, anxiety. It applied whenever I need to accomplish something non-trivial and is quite hard to counteract, though I mostly do nowadays. It does not apply to thngs I'm looking forward to and enjoy.
I guess as yours does the cause may be different, in fact from the little I know