It was pretty easy, once I thought about it a little. First of all, within the context of the dream I had, there had been a way to test whether I was in the dream- I just tried really hard to open my eyes. Granted, it wasn't a very good test. It's not always easy to wake yourself from a dream, and there's not much one can try if this fails, but it had worked.

Ultimately, I just told myself how useless solipsism is in a real-world context. We might all be trapped in the matrix, but if there's a way to test whether we're in the matrix and get out, then there's a way to define and test reality, and if there isn't a way to test if we're in the matrix and get out, then there's no reason to call what we're in anything but reality and accept the parameters of our shared experiences. In the latter context, saying that we might all be in the matrix doesn't predict anything or help us accomplish anything.

The most useful part of my experience was also what I found the most disturbing- that a piece of my subconscious knew something that my stream-of-consciousness self did not. It's a little humbling to be shown how much is going on in my brain that I'm not in on or aware of. I'm a lot less likely to trust my own perceptions, now.