Hi, I have been through a very similar experience as you had on your 30th birthday! This is what went on my mind: a) The urge to have sex. b) The inner restrain, which is also natural. c) Similar argument: Animals have sex...why not we? The issue is that for humans, sex involves a very special part of our existence, other than our bodies- i.e our psyche. Our minds are far more complex than thos e of lower animals, hence we function is a very different ways than them. As much as our bodies come in contact, so much or even more do our minds come into intimate contact. The human mind is a very complex "organ" and can get traumatized. This emotional trauma, results because of two very strong opposing forces: i) the instincts, ii) The conscience. The conscience evolves over several generations in human, and is deeply influenced by our familial, societial culture. The force of the conscience is as power and many times more powerful than the power of the instintual urges. So if we often go against the dictates of this consience (which is missing in lower animals) we tend to harm ourselves emotionally and in turn physically too. Hence, from these facts, human sexual behaviour is different.