Eye pain that goes away when i sleep what could this be?

Viral : Although other condition ie immunologic and inflammatory can cause especially if you are older, the most common would be a dna virus. Of greatest concern would be zoster shingles. Go see your medical doctor ENT or ophthalmologist.

Dry eye: Although there are conditions that need to be ruled out by your eye md, the most common cause is dry eye. Dry eye tends to cause increasing discomfort and pain as the day progresses only to be relieved with sleep. Your mornings are always the most comfortable with dry eye. Try using tears at least twice a day, around lunch and dinner. If this does not help you need to seek an eye md for exam.