'If we leave the economy will definitely go down hill very fast and no one from the rest of the world will help us.'
There are some very clever people supporting Brexit e.g. former Chancellors of the Exchequer Sir Nigel Lawson and Sir Norman Lamont, as well as big political figures of the past and present such as Michael Portillo, Frank Field, Kate Hoey, Gisela Stuart, Michael Gove etc
If any of them thought the economy would go down hill very fast, they wouldn't support Brexit at this point in time.
I think what is likely to happen if we vote Brexit, is that the EU will be finished because it will start a chan reaction across Europe and the existing European political class will be unable to stop the breakup.
Then what I think will happen is that the free trade rules and regulation will have to be maintained in order to keep business flowing, but it will be the end of free movement, laws made in Brussels, regulations on vacuum cleaners, plans for EU armies, anthems and flags etc.
So countries will all be independent again but will continue to cooperate for trade making use of the close ties they have built up over decades.
The European political class will no longer be making laws for all of Europe, but business will continue as before.