Hello~I wouldn't worry, you would have to have the tight headphones on for days before this happens, and I don't think that headphones could ever be that tight. An example of tightness that could cause necrosis are a very tight band around the arm, leg, finger, etc. First, though, you would hurt very badly in the area where the band was, then, it would start changing color, finally, the area would turn black. All this would take a few days and you would know it. Just sleeping overnight with the headphones really will not cause this, but, for the health of your hearing in general, I would not make a habit of it.
Your ears are hurting, yes, due to the pressure of the headphones, but, you have removed the phones, so the pain will eventually leave. Try rubbing the area that hurt, this will help to bring back the circulation.