Because when you lay on your side to watch TV or do something else, you have to lean your head back. With your neck tilted, your sight line is not at the identical level with the TV screen and your eyes have to adjust themselves. In this way, muscles of ocular region are in spasm and contract, which lead to an ache in your eyes, subconjunctival hemorrhage and water in your eyes.
According to your account of the situation, I can see that there is something wrong with your eyes. Generally speaking, people will not drop tears out of their eyes unless they face strong wind you know? So, it is possible that your eyes are infected but it is not a serious problem. Maybe it is that your eyes give reactions to some sources, such as light,etc. So you should visit a doctor and ask for professional advice.