That happened to me two days before my o/w when I was practicing in the pool. I was trying to do the fin pivot and I just plunked to the bottom all of a sudden and my right ear made a loud painful pop, and then it seemed clear. I don't remember any other symptoms. I stopped using a weight belt in the pool, and then everything was ok.
I still did my O/W two and three days later. I was a little congested, took Sudafed, took a little time to descend, and my ear felt a little weird, but I managed. After the weekend, I had a bad cold, and my ear continued to buzz and feel like it was infected.
My doctor looked at it a couple of weeks after it originally happened. He said I had baratrauma, he could see that my right "middle ear had bled out", and there was fluid in my ear. He gave me antibiotics, and the ear seemed to be ok after a week.
At the time, it seemed reasonable that if I could equalize in my O/W, then everything must be ok, and it's difficult to not do your o/w, something you've wanted to do for so long. Now I might reconsider, but now I have the equalizing thing down pat, and I try to prevent the problem by not putting myself in the position of diving congested.