(((lulu))) How traumatic! The good thing about it is, you are young. You have learned a valuable lesson and I doubt it will be played on you again with success.
Please be sure to send in a rebuff to your reprimands. By law they must be added to your file, and if the reprimands are shared with a new employer, so much your rebuffs. So make them tasty and to the point nicely for the new employer to read, ok?
I have much to say about how ppl react with new found power, but that isn't what you need to hear.
Alas! It doesn't sound good at all, and at holiday time too! Is there an organization that you can contact for support? What about complaints? Certainly both of the clinics' supervisors are under some licensing board... I would suggest checking with them to see if you have a leg to stand on. Plus, since the boss accepted your resignation, then you need to demand the 3 week's pay too.

It isn't uncommon to be released from attendance once a resignation has been accepted.
It would be interesting to see if the new boss fired you to put someone who is a friend into your position.
I agree that you should see therapy. Who better to help support you than someone who may have come through the same fire by trial as you? It isn't the end of the world, though I know it feels that way.
Come back and post more, or PM me if you wish.
PS I fully understand your wishing to give those patients a decent goodbye. I didn't assume you vented on them at all. From my perspective, what they received from you was less traumatic than if the admin had stopped by and didn't tell them anything but that YOU LEFT THEM.

This way, you told them yourself, being personal, and they were able to share their tears. They won't feel anger at you now, I'm pretty sure. If they do experience anger, it might be at the admin. Patients rule, and they will make noise if the new supervisor continues her ways.
I'm sorry you are in this predicament. If you don't find work soon, then don't beat yourself up over it...try and enjoy the days off ...really! Your next position might be very demanding!