Brief Answer:
Several possibilities....

Detailed Answer:
I read your question carefully and I understand your concern.

Twitching or as it is called fasciculations are contractions of small groups of muscle fibers. They can have many possible causes, most of them harmless. The most common cause is what is called benign fasciculations syndrome, twitching of muscles in different parts of the body, at times associated with other symptoms such as cramps, paresthesias etc but not threatening. The mechanism is unknown but it is often triggered or exacerbated by stress and anxiety.
Identifiable causes of benign fasciculations may be electrolyte disturbances, particularly calcium, potassium, magnesium. Thyroid dysfunction may also be a source of fasciculations.
Lastly there are the more threatening neuromuscular conditions like motor neuron disease, but usually preceded by a gradual onset over months of weakness and atrophy in the involved muscles, most commonly in one limb only later spreading to other areas.
So if the twitching persists a neurological exam for other possible neurological signs (altered and abnormal reflexes, atrophy etc) is advised as well as some routine blood tests (blood count, creatine kinase, electrolytes, liver and kidney function, thyroid hormones levels). Only if there are other neurological signs may tests such as electromyography (EMG) be necessary.

I remain at your disposal for other questions.

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