what are the symptoms of it?
An attack often begins with muscle pain, cramping, and stiffness. This is followed by weakness or paralysis.
Thyrotoxic periodic paralysis
An attack often begins with muscle pain, cramping, and stiffness. This is followed by weakness or paralysis 
what is thyrotoxic periodic paralysis? It is a condition featuring attacks of muscle weakness in the presence of hyperthyroidism.
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Thyrotoxic periodic paralysis [SEP] Signs and symptoms
An attack often begins with muscle pain, cramping, and stiffness. This is followed by weakness or paralysis that tends to develop rapidly, usually in late evening or the early hours of the morning. The weakness is usually symmetrical; the limb muscles closer to the trunk (proximal) are predominantly affected, and weakness tends to start in the legs and spread to the arms. Muscles of the mouth and throat, eyes, and breathing are usually not affected, but occasionally weakness of the respiratory muscles can cause life-threatening respiratory failure. Attacks typically resolve within several hours to several days, even in the absence of treatment.