Adrenilin can mask allot of pain. If your adrenilin leavels, or blood sugar levels are low you can feel allot more pain .while your adrenilin levels are high you matabilise sugars rapidly and can cause people to feel sick and lightheaded, this usually happens only the first few times, soon your body tunes itself to allot of nerve stimulus. As for the comment about staying out drinking late the night before can make an effect, It sure can, especially if it was the Tattooist. Hha

I like the basic structure of your tatt, but looks a bit spaced apart, would look awesome with some backround like an underlying image. Some uniformity of the shading would look better though.