In most cases, no signs or symptoms of susceptibility to malignant hyperthermia exist until you're exposed to certain drugs used for anesthesia. Signs and symptoms of malignant hyperthermia may vary and can occur during anesthesia or during recovery shortly after surgery. They can include: 
Severe muscle rigidity or spasms
Rapid, shallow breathing and problems with low oxygen and high carbon dioxide
Rapid heart rate
Irregular heart rhythm
Dangerously high body temperature
Excessive sweating
Patchy, irregular skin color (mottled skin)
 In rare cases, people at risk of malignant hyperthermia have shown signs of a reaction after intense physical activity during excessive heat or humidity, during a viral illness, or when taking statin medication used to lower cholesterol. If you're at risk of malignant hyperthermia and you don't have a serious reaction during your first exposure to certain anesthesia drugs, you're still at risk if you receive these drugs in the future. Other anesthesia drugs that don't trigger a reaction can be used instead.