Wings, I have experienced that....

There is a point, which is hard to always find and doesn't always happen, where my system overloads basically and shuts down, which results in getting tighter and normally going completely dry. That point can happen for a couple of different reasons... either too many orgasms in too short a time... or too long trying to get to the initial orgasm (It and I both get bored then... lol).

Normally a good amount of lube and a few painful strokes can get it back to fun but not always, sometimes it is just better to throw in the towel... so to speak.