I have no idea what may be causing the cramping - - but if this were happening to me, I would start by eating a banana before bedtime to see if it helps at all.

Bananas are known for having a healthy does of potassium - - and sometimes charlie horses are caused by an electrolyte imbalance.

As far as cramping and MG - - perhaps someone else can shed some light on this . I have never experienced cramping - either from MG or mestinon.

Sue