What you are experiencing is an entirely normal reaction to shock, honey.
Part of you can't believe what happened, but part of you knows only too well that it did happen, and that it - or worse - might happen again if you allow him to creep back into your life.
There's little to be gained by trying to fathom why he did what he did. Ultimately, he did it because he could and because he's got a history of doing it and getting away with it.
If you're feeling no better in the next couple of days, make an appointment with your GP with a view to getting some medication that will alleviate panic attacks with possibly a short course of antidepressants and a little something to help you sleep.
Once again, I would urge you to get back in contact with the police to report the sighting you had of him outside your home the day after he attacked you, and tell them what you know of his history.
This will serve several purposes: it will go some way to enable you to put the matter 'to bed', as it were; it may provide a solution to the question of returning the item he's left in your home; and, most importantly, the police will have an account of his behaviour on that night which won't fall into the general category of 'couple had too much too drink, argument ensued'.
Should he put in another appearance or make contact with you, the latter will be of immense value as it's so easy to omit/forget or give a less than an accurate account when one's fears/emotions are under stress.
For my own peace of mind, can I ask you to please check into your thread on a daily basis for the next week or so? Otherwise I fear that I'll lose sleep wondering how you are faring 
All of this notwithstanding, I sincerely hope you and your ds have a good weekend.