Leg cramps can happen for a number of reasons, but rarely are they serious when they occur without other symptoms. Given that yours also could be associated with diagnosis that you have of fibromyalgia, you should mention them to your doctor
. Cramps in the legs are thought to arise from some sort of nerve stimulus that leads to repeated firing of the nerves and muscle contraction. There are many ideas about what the initial stimulus to the nerves can be, and there are many factors that can be involved.
As people will often have cramps during or after periods of time when their limbs have been in a certain position for an extended period of time, that could explain the cramps that you are having at night, as one's legs are often in abnormal positions during sleep. Other causes of cramps include shifts in the levels of molecules and fluids in and out of cells, as with dehydration, although that is less likely to be the cause. Given your other symptoms and medical history, as well as the fact that you are taking daily medications, please discuss your symptoms with your primary care provider and the physician who prescribes your medications.