it could be a sti ....i dont know how to spell it...but i wake up with my eye swollen and alittle red and very painful....a sti is something caught (a small granule of something) and over the night your eye tries to protect itself from the outsider (almost like an oyster making a pearl) i suggest you take luke warm water tip your eye upward and try and get some warm water inside your eye....also put your face in the sink and cup your hand with water and submerge your eye in your cupped hand and keep blinking...its the only way it will get out.....you know its a sti if your eye is swollen.....if its not swollen its probably from a headache