Hi waterknob, well it is good that you're going to be getting someone else in to help, hopefully they'll be able to take the weight off you a bit
But for now.......well if your clerical duties are slipping you'll at least have some evidence of the other things you've had to do which have needed to take priority. And perhaps when you're asked to do something not clerical then make it clear to the person asking/expecting that you can do it, but that means you'll be further behind on............and you know what I'm going to say now...............document it!!!!
And make sure you're telling your manager the problems you're having fitting in x, y and z, keep telling them!!! Including breaking down the time it takes to do certain things, they can't expect you to break time barriers/work miracles, right??!! And again.......document conversations!!
When everyone else is in the same position as you though.........reality has to kick in at some point with the managers..........if it's not just one person/you not being able to hit targets given the restraints, which it won't be!!!
And you know, why not tell that junior manager some of the things that might be contributing to your chest pain, shortness of breath...........the stress and pressure you're all under (??)........how you're trying to do your best..........how you're doing everything that's physically possible but............
And don't be sorry for the language , you feel strongly about something.........you express it!!! Just glad you're feeling a bit better on posting though, hoping it continues........and don't forget we're here for you!!!

Alison