A muscle spasm — also known as a charley horse, muscle cramp or twitch — is a sudden, involuntary movement in one or more muscles. Common causes include stress, exercise, or dehydration, but nerve ...

Hemifacial spasm (HFS) is a rare movement disorder that causes involuntary muscle contractions on one side of the face. It typically starts with painless but annoying twitching around one eye. Over ...