Assuming the sagging doesn't reach down to your knees(!), I know of something which sounds a little bizzare, but which may help to temporarily firm/tighten the skin. Buy a tube of PreparationH (haemorrhoid) gel. Apply a very small amount of the gel to the affected area, avoiding contact with your lashes/brows. This can also be used for the 'puffy' eyes we sometimes have in the mornings. It sounds a very odd thing to use around the eyes, but apparently, many beauty therapists include it in their kit.