Oh dear God....now you are going to have to chill. grin
First, you are not having a heart attack. Period. End of mortal threat discussion.
Second, the anticipation is what's driving you out of your mind (metaphor only, grin). The "build up" - the "how can I do this??" the "I can't PICTURE myself doing this every single day, the streets, the buildings, isolation, all those people, having to go to work, then having to come home in the traffic, and what about the elevators, I can't see how I can do this every single day..." Stop.
It is impossible to picture EVERY single day in your future and fathom how you can "do it" - in the reality of doing life, you will be encountering one moment at a time, not an onrush of overwhelming challenges the way it seems in your mind.
Think of a movie preview - in less than a minute, they are slamming images and sounds at you to give you a "taste" of the 2 hour film - each image stays on the screen for only a few seconds, with frantic jumpcuts to the next image, no through-line, no evolving of the plot...just rapid image after image, firing away to give you a "feel" for watching the film. That's what you're doing to yourself. You're living every hour with "Coming Attractions" of My Life In Melbourne - rapid intercut scenes with loud sounds and bright flashing edits that are jarring to your entire system. Those previews are meant to be watched for 30 seconds - you're "watching" yours every hour for the past several weeks. Seeing the actual MOVIE (living the actual experience) is not going to be like this intense preview experience you're torturing yourself with.
Secondly, go to Melbourne. You will never know if you don't go. Give it a try. If the worst happens, and you cannot do it without intense stress, you can come back. (Do not start on the "HOW could I come back....I'd be a failure, my parents would never let me come back!!" IF you had to come back, you'd come back. Period. Do not even "go there" in creating another horrible preview of THAT scenerio)
You are tormenting yourself. And the entire overwhelming feeling is nothing but anticipatory anxiety.
You have BEEN to Melbourne. You have walked in a big city before. You are not moving to Iraq or Neptune. This is not going to be ANYwhere the horror you imagine it to be. And no amount of imagining the worst will HELP. It will only make you more and more anxious.
p.s. In one way, you ARE having a "heart attack" grin. You are having a symbolic "attack of the heart" because part of you is so emotionally connected to your family - and you do NOT want to grow up - part of you wants to and part of you doesn't want to ever give up being taken care of. Now....it's even more complicated than that. Part of you doesn't want to let your family off the hook so easily! It's THEIR fault you aren't more secure, so damnit they should have to pay for it by being your support forever!
Dark angry thoughts and lots of conflict about growing up. That's what your "heart attack" is made of.
Peace,
Janine