Thank God you are all right.
I did 20 Lf'es so far and I praise ES. It is very unfortunate what you have experienced.
My token on why it happened.
I agree with the other poster it was accumulation of the problems. I would not be surprised if you have some type of adrenal fatigue in which there is mineral imbalance, usually terribly in favor of potassium insted of proper balance of sodium-potassium. I did my hair mineral analysis and that's exactly what it showed: low sodium, high potassium.
Next. We don't know maybe paragone herbs had some influence on that bad reaction and ES just topped the glass off.
Third. Constipation stopped the traffic in the GI and because of that instead of normal water absorption through the intestinal villi and going to the liver what happened is that because of traffic jam in your guts ES water was pushed forcefully way too fast and the massive amount of mgso4 went srtraight to the blood. And here your body did what it should have done: to expell ecsess ES as soon as possible and in this radical case, as with high force as possible. And here you have deadly mix: your sodium levels are already low, aldosterone (which is responsible for mineral balance and which can't be produced in sufficient levels because of exausted adrenals) is alsmost nonexistant and pretty much ALL sodium was being forced out very very fast. And as we know, no sodium= no life. And of course your body was desperatelly trying to manufacture aldosterone in massive amounts, but just could not. Additionally, remember, you had loose stools before you got constipated and if you did not replace sodium bingo- you were already moderately-severely sodium deficient. And if a person has even slight adrenal fatigue it is a very very big mistake to restrict salt intake, which only further deepens the problem. Sodium restriction, telling that you don't need sodium that your body takes care of that- is a possible deadly mistake of some health-conscious diets. Salads, olives, etc. have ridiculously low levels of sodium. It took me a long time to figure out why I often was going after roasted nuts not being too hungry and it was I was going after sodium! not nuts. And if at least in part of all that I said here relates to you I am sure all of it at least contributed to the violent reaction of your body.
In all due to these unfortunate accumulative events it was too much for your body. Normally, body easily should take care of the problem and this emergency situation teaches us a lesson that despite it is natural thing, we should keep an eye on everything we do.