I was awake all last night with severe nausea and vomiting. However, there was nothing in my stomach to come out, so at the end of each nausea-vom cycle (which typically lasted anywhere between 1 and 2 hours) all that came out was a small amount of dark grey, almost dark blue slime in some clear mucus. Why was it this color? I had thought it was bile but have since read that bile is bright green. Should I be worried?