Karl, I wouldn't worry about one pill too many, we all do this, sometime intentionally to get an extra boost, but in the event you forget and take several here is some info

from Family Health Information.com

Overdose

Too much Sinemet CR may cause muscle twitches, inability to open the eyes [including sleepiness], or other symptoms of levodopa overdosage. After taking Sinemet CR, if you feel that overdose is suspected, then contact with your doctor immediately.

and from InhousePhamacy.com

If you take too much - Overdose

In the case of severe overdose, the treatment is basically the same as with severe overdose with treatment of Levodopa used alone. General first-aid measures should be carried out in addition to immediate gastric lavage. The application of liquid intravenously must be measured and air passages must be kept clear. Adequate electrocardiograph control should be carried out to permit the prompt detection of the development of the arrhythmia. The possibility that the patient may have taken another medication at the same time as Sinemet should be taken into account. As yet, there has been no research carried out regarding dialysis and thus it's possible application in the case of overdose is unknown. Vitamin B6 will not affect the action of Sinemet.