Muscle Strain: This is the most common cause of muscle spasm, often resulting from overuse, injury, or sudden contraction of the muscle. It is frequently seen in athletes or individuals who engage in strenuous physical activity.

Dehydration/Electrolyte Imbalance: Dehydration and electrolyte imbalances, particularly hypokalemia (low potassium), hypocalcemia (low calcium), and hyponatremia (low sodium), can lead to muscle cramps and spasms.
Overuse or Fatigue: Prolonged use of a muscle can lead to fatigue, which may cause muscle spasms.
Musculoskeletal Conditions: Conditions like tendonitis, bursitis, or stress fractures can cause pain and lead to muscle spasms as the body tries to protect the affected area.

Tetanus: Although rare in areas with good vaccination coverage, tetanus infection can cause severe muscle spasms, including the characteristic lockjaw. Missing this diagnosis can be fatal.
Neurological Conditions: Conditions such as multiple sclerosis, peripheral neuropathy, or spinal cord injuries can cause muscle spasms. These conditions require prompt diagnosis and treatment to prevent further neurological damage.
Compartment Syndrome: This is a serious condition resulting from increased pressure within a muscle compartment, which can lead to muscle and nerve damage. It is characterized by severe pain, especially on palpation, and can be a medical emergency.

Dystonic Reaction: A rare but potentially life-threatening side effect of certain medications, characterized by involuntary muscle contractions.
Strychnine Poisoning: A highly toxic substance that can cause muscle spasms leading to rigidity and death if not treated promptly.
Hypothyroid Myopathy: Muscle weakness, stiffness, and spasms can be associated with hypothyroidism, although this is less common and usually part of a broader spectrum of symptoms.