Lost Firmness After Three Days in Chastity O.o

I’ve just completed three days in chastity. It was a tough journey, but I survived. On the evening of my release, my girlfriend treated me to an amazing tease session ^_^… My question is this: when she untied me, I noticed that my balls swelled up by about 25-50% (I’m accounting for some paranoia here) and felt quite soft… Everything still functions properly, but I’d like to understand what exactly happened????