con·vul·sion 
(kən-vŭlshən)
(kən-vŭlshən)n.
1. An intense, paroxysmal, involuntary muscular contraction.
2. An uncontrolled fit, as of laughter; a paroxysm.
3. Violent turmoil: "The market convulsions of the last few weeks have shaken the world" (Felix Rohatyn).