What Causes Sudden Numbness On Left Side Of Face And Arm?

A month ago I was sitting on the couch and for about 3 seconds the left side of my face got really tingly, almost numb, as did my left arm. I also got really lightheaded. I went to the ER where they did a carotid scan of my neck, results came back normal. They also did a CT scan, results came back normal. I was directed to a neurologist who wanted to do blood tests to see if I have Lupus, or blood that is susceptible to clotting. All results came back normal. Around the time I had my ER visit I noticed that whenever I tilted my head back I got a headache like pain at the top of my head. I also since then have been experiencing dull headache pains all throughout my head. Since the ER visit I've still had the tingling in my face and a little bit in my arm, but not as severe as it was that day.