Assuming it is true myotonia, since it runs in multiple generations of your family, it is likely a dominant myotonia causing disorder, and thus could be Thomsen Myotonia Congenita, or a sodium channel myotonia such as paramyotonia or acetazolamide responsive/potassium aggravated myotonia.

If you have the warm up effect and it gets easier to move with movement...at least until you sit back down, and you do not have any profound or progressive weakness in your family, it's likely Thomsen Myotonia Congenita.

Type of Myotonia: Becker

Country: USA

I feel nauseated when my stomach muscles cramp.

Type of Myotonia: Thomsen's

Country: USA