What is the meaning of convulsion?

noun

• A sudden uncontrollable attack.
  • usage: "a paroxysm of giggling"; "a fit of coughing"; "convulsions of laughter"
  • synonyms: paroxysm, fit
• Violent uncontrollable contractions of muscles.
• A violent disturbance.
  • usage: "the convulsions of the stock market"
  • synonyms: turmoil, upheaval
• A physical disturbance such as an earthquake or upheaval. .