What causes sudden jerking or twiching of muscles? It this something to be worried about?

The etiology, severity, and cause for concern in regards
to a sudden muscle twitch or jerk depends on which muscle is experiencing this, how
often is this occurring, what is the duration of the "twitch", and is there pain or
discomfort associated with it. I will assume the twitch is only an occasional event of a
few seconds duration with no pain involved. In this case, the cause could be from a
number of factors like over consumption of caffeine, mild electrolyte disturbances, or
even emotional stress.

Generally speaking, when a muscle
twitches the underlying problem is not a muscular one, rather it has a neurological
origin like a mild neuritis of the nerve that innervates the particular muscle that is
twitching. This could be due to an over stimulation of the nerve, an inflammatory
process, hypocalcemia, hypokalemia, hyponatremia, or a B vitamin deficiency. This could
also be due to a more serious underlying neuromuscular
disease.

I encourage you to consult with your physician if
the frequency or duration increases or if pain is experienced with the
movement.