That could very well be a reaction to the cleansing it is doing to your liver/gallbladder. Cleansing the liver can release intense sadness or even rage, sometimes anxiety. Ease off the dose a bit until you can maintain your comfort zone.
About 1/2 cup in the enema solution should do you just fine. Ideally, do a plain salted flushing enema first, then try to retain the ACV enema for 5 minutes or so. If you're pressed for time, just do the ACV enema.