You can get stiff muscles after heavy lifting, exercise or during a cold/flu. Stiff muscles, especially in the jaw/neck/stomach can be a sign of tetanus. Other signs can include difficulty swallowing, muscle spasms, sweating and fever. Pain or stiffness in the neck, back and legs can be a sign of polio. Other signs are fever, sore throat, diarrhoea, headache, stomach ache. Only a trained health worker can give you correct diagnosis and treatment.
Attribution: Straight Talk Foundation & Marie Stopes