It’s kind of unusual for Hamlet to interrupt himself so much like this. I mean – not unprecedented – certainly some Foh! About my Brains! Turns up earlier. But he’s interrupted himself twice in this same passage.
Well, he’s got a lot on his mind, certainly and a great deal of unease. So it does make some sense that he has some emotional outbursts.
Also – side note: I would love to find occasion to use “larded” as it’s used here. It’s so beautifully specific. Like – the letter is overloaded with reasons and the reasons are laid on thickly, like a layer of fat.