Not a silly question. I've seen 'sugar free' ones before so I assume they contain less syns.
Also, do they have the nutritional information on the side of the bottle? Calories, protein, carbs, fat etc? If so, you can use the calculator to figure out the syns or post the info on here (with the serving size) and someone can calculate it for you.
But, to be honest, if you're ill - you're ill. I say sod the syns and take the medicine if you need it.