A droopy eye (meaning a drooping especially of the upper eye lid) is called ptosis. There are many things that can cause ptosis, but most of them involve compression or inflammation of the nerves that supply the eyelid. By interfering with the visual field, ptosis alone can cause blurred or double vision
Although some of the causes of inflammation of the nerve leading to ptosis are not serious and will resolve gradually, there are more serious causes that need to get ruled out. For this reason, this condition should always be checked out by your primary care doctor
as soon as possible.
I am also concerned about your painful eye. This, to me, raised the ante on what could be going on. If the eye is just a little bit irritated or dry, this might simply be from interfering with the normal blinking action of the eyelids and might be remedied by eye rewetting drops and is probably not too serious. However, if you have true eye pain, eye redness, or any other systemic symptoms (like fever
or facial swelling) these suggest that there may be a more serious problem, such as an infection, underlying your symptoms that should be emergently evaluated by a doctor.