What Causes Prominent Painful Vein In Palm Along With Dizziness?

A vein in my left palm turned blue and painful. I have dizziness since last week. I have been dehydrated too. I didn't drink enough water for the past few days! Today for a moment the dizziness got so bad that I fell down! Then I realized I was dehydrated ! I am worried about my palm and vein! It happened few times before and only on my fingers!