Watery eyes are quite common in the daily life and can be the result of many a cause. As far as I am concerned, dry eyes, clogged tear ducts, conjunctivitis, allergies and many other environmental irritants may all lead to watery eyes. You said your eyes water when you are sleeping and I am sure that you can check whether one of the above-mentioned reasons is the main source. By the way, over-the-counter remedies such as artificial tears and medicated eye drops can help release the watery eyes. If your eyes keep watering for a long period of time, it's the right time for you to see the ophthalmologist.