I have something that sounds much like what you seem to be describing on my wrist too and it freaked me out for a while. Physician confirmed that, at least in my case, it was a ganglion cyst as you mentioned, which is not generally harmful.
She also confirmed that they can appear, get bigger or smaller, or even go away randomly over periods of weeks, months, or years, so treatment isn't really worth it since even if drained it can just come back. If it's really bothering you I was told one can just smash it with a large book to pop it-- hurts a lot, but it's actually probably more effective than draining it since it actually breaks the cyst. I accidentally popped mine when I flipped over on my bike (lol), but it came back a couple years later.
Ultimately, I would suggest not worrying about it but if it does continue to be a concern, particularly if it begins to hurt, then see a doctor.