A person who feels his or her eyes are heavy has a condition called eye fatigue, which can be caused by long periods of driving, reading and staring at screens and devices. This may cause discomfort, change in vision and double vision.
Eye fatigue is not a serious condition as it can get better on its own after resting or avoiding habits that cause it. At times, eye fatigue can be a symptom of an underlying health condition so visiting an eye doctor may be necessary. It is estimated that eye fatigue affects 50 to 90 percent of computer users, as stated by WebMD.