Feeling shaky is a symptom of hypoglycemia. At what value you feel the effects of a hypo is different for everybody. A recently diagnosed diabetic (or a diabetic with poorly managed glucose levels) will feel the effects of a hypo with a much higher BG than a long time diabetic (or well controlled diabetic).
You may feel a bit rough for the rest of the day after a hypo or with fluctuating BG levels, but normally once you've eaten something to bring your BG up - the shaking disappears once your levels have stabilised.