In reality, there is a close affiliation between these two phenomenons. The major reasons are formulated as below. First, as we get tired, the tear duct will produce less fluid, which dries out your eyes. It stimulates the tear ducts when you rub your eyes, and spread moisture over your eyes. Second, tiredness also closes your eyes, so you may rub to keep them open. Finally, there's a connection between the muscles that move your eyes around and your heart. It also has effect on ocular muscles. While you are also putting pressure on your vagas nerve, it could reduce blood pressure, a reflex slows the heart. This might be relaxing if you feel very tired.
