Lactic acidosis is a side effect of Metformin in unusual cases and is serious. Metformin needs to be taken with food.
As waverider stated, there may need to be adjustments in the doseage of the Metformin. There are pill-splitters available to cleaning divide the 500 mg metformin into two equal 250 mg doseages.
Whoever "told you" that you cannot reduce your blood suger to levels affecting functioning with Metformin is misinformed.
That being said Metformin is an excellent medication, well-tolerated by most patients.
No diabetic medication should be administered without the availability of a glucose meter, and testing, with the availability of a simple sugar (orange juice, for example) to handle hypoglycemia readily available.
There are arguments against taking Metformin before going to bed, because the hypoglycemia may not be noticed in the sleep condition.
For some people, Metformin can cause glucose [blood sugar] levels to drop too low [hypoglycemia]. This often times happens when Metformin is combined with other diabetes medications, and is more common in elderly folks or folks with internal organ issues. Low glucose also can happen when fasting before surgery or a blood test/s and after lengthy exercise.
You should notify your doctor of your low glucose experiences ASAP. Ask your doctor how to adjust your Metformin dose if needed. Do not change your medication dose or schedule without your doctor's advice.