Okay, so this is what happens when you think "hey, my apfelwein has near stopped bubbling. What should i do now?" Then your twin who happens to be thinking the same thing goes "how about yeast nutrient!" Thinking i put in a squee bit too much.
By the way, the bung is still in there.
(No comments on the dirty kitchen, i know i need to do the dishes.)
you didn't add too much,(probably) the crystals of the the nutrient just disrupted the gas that was in suspension and released the gas. Just like mentos and soda. I had it happen to me once and now I just dissolve the crystals in some water or juice and then add to the must.
It does make a glorious mess tho doesn't it!