Thanks for writing to us.
From the description provided, it could be a ganglion cyst
. Ganglion cyst are quite common in wrist area and have a tendency to appear or disappear on its own.
As the lesions has subsided, I do not think there is a reason to worry. Once the lesion reappears during a course of time, you may get it examined by an orthopedician for evaluation and further management.
Hope that helped.