Paige, as you read through the posts, almost everyone lists the type of myotonia that they have. It shows up at the end. You can do a search or just scroll through the posts. I would expect at least half of the people on this forum have Becker's MC.
Yes, I have Becker MC, and weakness has always been a complain of mine, more so as I've gotten older.
My initial diagnosis says "atypical myotonia?" because I complained about intermittent weakness....and also because I described the warm up effect in a little more detail than the doctor had previously read, I think.