Possible Clues:

• Involuntary muscular movement
• Muscular misfire
• Sudden involuntary contraction of a muscle
• Fit, but writing up to health resort
• Crick in one's neck, e.g.
• Contraction of springs on mass
• Pretend to have (injury)
• Spell differently the contents of 2
• Something you can't control
• It can cause one to be a real jerk