Do you wear contacts lenses? How is your vision? Do you sleep with a ceiling fan on?
There are several causes for eyelid swelling. The most common, as you have already eluded to, are allergies, sinuses.
Another common cause is giant papillary conjunctivitis. This is a condition that we see often in contact lens wearers. The eyelids develop these giant papillae (bumps) that can be seen when the upper lids are everted. This is usually caused by overwear of contacts or reaction to contact solutions. This becomes a chronic problem. It can be controlled by drops like Crolom.
Finally, because the skin around the face is very loose, when you get an episode where you have swelling it can often become chronic. Even though the precipitating cause is gone, the loose skin allows for fluid to fill back up very easily (such as when laying down due to gravity). Once you have eyelid swelling, it may take steroid medications to resolve the chronic swelling.
I hope this helps and thank you.