Night

• Most leg cramps at night are from involuntary contractions, and according to MayoClinic.org are generally not dangerous. Seek emergency care if you have diabetes or peripheral artery disease (PAD), toxin exposure, or if the pain is severe and does not stop.
  
  

Strain

• If you have been exercising, wearing high heels, running, climbing stairs or hills, or doing activities that puts a strain on your calves, it is probably not an emergency. If resting does not relieve the pain, consult a doctor.
  
  

Not Moving

• Stretch and walk to avoid blood clots on long flights.Image by Flickr.com, courtesy of Andrij Bulba
  
  Sitting on a plane or elsewhere for a long period of time with sudden calf pain may indicate a blood clot and emergency situation, particularly if you have underlying medical conditions such as recent surgery, PAD, or a previous history of blood clots.
  
  

Acute

• Sudden calf pain may be a blood clot (thrombus), an emergency that requires screening for deep vein thrombosis, because the clot can move to your lungs and cause a pulmonary embolism.
  
  

Symptoms

• Although only half of the people with a blood clot have symptoms, MayoClinic.com says symptoms may include calf pain in one leg, ankle, or foot inflammation and redness.