hello sarah*** thanks for your question you are experiencing severe one sided pain near your eyebrow which goes into socket and is tender. Usually there are a lot of causes of such type of pain as Throbbing pain of migraine, Excruciating pain of Cluster Headache.. you are having this pain in night so it is very less likely to be migraine or cluster headache. so as per my opinion the reason of pain is in left eye its self. If its a deep sharp pain behind eye and which worsen with movement it may be due to inflammation of nerve route of eye. But usually such pain is associated with fever and other symptomatology of eyes. Then most likely the cause of your pain is eye strain which is leading to sore muscle of a particular direction in eye and with continuous strain it is persisting and it is tender to touch. accommodation spasm is also an another cause, spasm or fatigue of muscles that are involved in accommodation is also a possibility. and third possibility is glaucoma, which is in simple terms increased pressure in eyes and which causes pain, it is unilateral pain and is severe and is usually precipitated by darkness and is associated with redness of eyes and exacerbated by eye movements. Blurred vision is also a symptom. Last possibility is conjunctivitis which is a infection of conjunctiva of eye, but its usually bilateral and severe pain is not there. So dear friend there are chances of Neuritis, glaucoma or accommodation muscle strain, and kindly don t neglect the pain and visit a good ophthalmologist for advise. Till then apply hot fomentation on affected eye and for pain you can take simple OTC drugs. TAKE CARE THANKS HOPE I SOLVED YOUR QUERY KINDLY RATE