What Causes Pounding Of Heart,severe Headache And Nausea?

Feeling really weird: My heart is pounding (not exactly racing, but I can feel it beating forcibly throughout my body); my head is killing me. It s not a migraine, but the pain is almost unbearable. I m super nauseous; no abdominal pain, just very queasy. I m trembling, but not cold. Been feeling like this for hours. Ate plenty of calories and have had tons of water + some coffee today. Any idea what s wrong?