I wonder if he just wants everything to be like it used to be and is accepting when mum is fine, but when it blows up he then can't cope? I think thats understandable in some ways, dealing with changes like this can be overwhelming and its easier sometimes to think that it will all just go away ...what happened was a one off ..so to speak.
I think you are going to have to have a hard conversation with your dad, because although you know this is going to be a continuing problem, I am not sure by what you have written he does. As in letting her pick up her own medicines, thats not going to work unfortuantely, no doubt he means well by your mum, but really he isn't helping although he had good intentions and probably doesn't want anything to change if he can help it.
The lorazepam may help, but it may not. Some people though sedated can still swing into action full on, just to warn you. It may be that you have a quite night, hopefully.
You can't manage these scenarios continuously from a distance and your going to have to broach this with your dad and talk about the way ahead for all of you.
Hoping you have a peaceful night