This is perfectly normal. If the session is long, even several hours, this is for the body as a big shock, namely, that they must tolerate the pain or extract Endorphin is a natural to make the most reduced and mitigated. After tattooing you could be a little tired, then might even little spinning in your head, you are sleepy or the like; but there is a very pleasant satisfaction of the obtained tattoo. It is best to eat something again (like before the tattooing) and at least a few hours rest.
Tattooing-Pleasant Satisfaction