I think I have a slightly different view on this than the majority of PP. But I will preface this by saying I'm not intending to sound judgemental and it's meant with absolute kindness.
You were obviously shocked by your DC's aggression - and understandably so. But in your own words, "screaming" and "crying hysterically" to the extent that people outside came "running over" is quite an extreme reaction. It suggests that you're really struggling - and not really surprising given everything that you've been through.
It's awful when young children act aggressively and it IS really shocking. And of course it's normal to feel emotional about it - we're not robots.
I have twins who are both autistic but my DS has pretty high needs. When he was a toddler, he bit everything and due to his frustration, sensory difficulties etc, he used to lash out all of the time. I can't count the number of times I've been slapped around the face, hair pulled, head butted, and bitten. He's broken my skin many times - and it's been infected too. I really would second advice about getting it checked - human bites are nasty. I've been head butted so hard I thought he'd broken my nose and jaw (separate occasions). My DS wasn't verbal for a very long time and he couldn't process the world and his emotions. But it was so very hard to distance myself from the attacks. Last year he kicked me so hard in the stomach that I needed a CT scan and a trip to A&E - but in general he's the sweetest, kindest child you'll ever meet and he adores me.
I'm only saying all of this just to say that I really do understand what it's like. It's awful and overwhelming and just so bloody hard. There are still days when I sometimes feel like I can't take any more physical assaults (although nowadays - aged 12 yrs old - they're usually due to clumsiness rather than the rage attacks of his younger years).
You've had some really good practical advice on this thread about wrist reins and also the advice about not pulling away, but leaning in and making him immobile. Keeping my son out of roads was often the trigger point for us too.
Lots of us have had days when a toddler's/child's behaviour has driven us to tears. But your description of "screaming and crying hysterically" requiring others to "run over" and help sounds like a woman who's really at breaking point. There's absolutely no shame in that at all, especially with everything you've been through.
Also, some of your follow-up comments suggest that you think your child understands what they're doing. As others have said, at their age, they won't have the cognitive ability to understand consequences just yet. Your child is lashing out but not deliberately at YOU - it absolutely could just be those awful toddler years, it could be due to the loss, or there might be some SEN there. You mention your 2yr old shouting "just shut up everybody" - that sounds like auditory sensory distress, potentially.
Has your DC had their 2 yr check yet?
Your GP really isn't going to judge you but I really think you could do with seeing them. You can get your bites checked, have a conversation about your DC and have a talk about how you're feeling in yourself. Of course there's no magic wand to make everything better, but you've been through so, so much and if this happens again (which it probably will if your DC is going through this phase or SEN) you need to be in a position where you don't end up at rock bottom.
I can't tell you the times I've sat and cried my eyes out in the GP surgery. A few weeks ago I even told them on the phone that I didn't know how long I could keep on doing this. It can be bloody hard to keep going when you're struggling. Your GP is there to help you, not judge you - and you absolutely deserve some support. There's no shame at all in that. I promise you they will have seen many mums feeling overwhelmed and not coping, even without all the trauma you've experienced.