You may have a mild to moderately strained gastrocnemius muscle. Potassium is not going to be an issue. Certainly, hydrating yourself is never really a BAD thing (as long as not taken to extremes) but rarely does that alone or the eating of bananas or the other folklore about Gatorade, etc. ever really work. These kinds of pains can come in people not suffering from any imbalances metabolically in anything. As I said, if calcium or potassium were a problem to the extent that the calf muscle suddenly had a spasmodic pain radiating to the knee then, the expectation would be many more muscles would be involved. This sounds to be musculoskeletal, circulatory, or something unknowingly post-traumatic in terms of either a blunt or a stretch injury of a tendon, ligament, or muscle belly tear which can occur in folks with very severe OSTEOARTHRITIS- not so sure that your FM is playing a role due to the location. Send more questions to www.bit.ly/drdariushsaghafi and I ll be happy to answer. At any rate, have your primary doctor do a good physical examination on you, correct any metabolic issues they may find, and then, consider stretching or physical therapy types of focused activities for that particular leg and see where that takes you. If your primary doctor feels that a specialty exam such as a DOPPLER study of the leg is necessary just follow their instructions.