Glassy eyes indeed make people look listless. There are many factors which might cause glassy eyes. Elevated thyroid level can cause glassy eyes. It is called Grave's disease too. It is a disorder of our immune system which produces too much thyroid hormones. Eye viral infections, such as Conjunctivits might cause watering eyes and reder eyes glassy look finally. Chickenpox or shingles also make it possible for people to get glassy eyes. It might be associated with hypoglycemia, which means the blood sugar level of patient is lower than normal standards. Besides of glassy eyes, hypoglycemia can cause other symptoms such as visual disturbances, blurry vision, cognitive behavior or even seizures in some rare cases. It is also possible that your glassy eyes are caused by some certain medication which is usually used to depress central nervous system. Normally speaking, glassy eyes are not a big problem. You can check all the causes stated above, and see if any fit your situation. If needed, visiting a doctor at your earliest is a smart choice.