For me, when I'm channeling, it is one of the most calm feelings I've ever experienced. It's like being in a daydream, but more aware. Hard to explain. It took me years to realized that I was channeling, and it wasn't my own thoughts, so it can be difficult to differentiate at first. Again, for me... it's those "thoughts" that come to me that make perfect sense, and just seem to come out of nowhere. They are worded well, and make me sound like i know what I'm talking about, lol. Without my channel, I'm not nearly as intelligent sounding as I am, because my brain goes numb and I turn stereotypically blonde.
It started for me as what seemed like normal thoughts, but once I realized it wasn't, (I had an "aha" moment, which is another sign your channeling), I started writing it all down. From then, I have been able to differentiate 2 separate channels, which often work together to give me the information.
I've channeled my whole life, but I've only KNOWINGLY channeled and written it down, in the last 5 years.
So, all i can really say is to pay attention to the type of thoughts you have. If they are unusual, or they don't fit what you would normally think about, then you are most likely channeling.
Here are 2 articles I wrote on channeling from my own personal experiences.
My Channel: How It Works For Me - Wake up and Unhypnotize
Channeling: You Do It And Don’t Even Know It - Wake up and Unhypnotize