I have some sort of swelling or lump or something under my neck. It's not a hard lump or anything. It's really soft and squishy. At first, it was just on the right side, but then yesterday there was one on the left side as well. Ever since the first one appeared (about a week ago), I've experience extreme lightheadedness several times through the day, to the point of feeling like I'm about to fall over. I'm also extremely tired, and it takes me forever just to get out of bed in the morning. What could be causing this?