If it is due to insect bite like mosquito, the eyelid can be itchy, not typically painful, and often there is a red dot where the bite occurred. Sitting or standing helps the fluid move and the swelling gets better.
This happened to me a few mornings in a row. Eyes glued shut upon waking. Got progressively more irritated throughout the day as well. Eye doctor said it was viral, and suggested nothing more than lubricating eyedrops every 30 min for 3 days while awake. Hope this helps. It did for me by the end of the first day.