The muscle contractions are only one aspect of an orgasm. There is also a release of hormones in the body that cause chemical changes in the brian, which consequently effects how we feel.
Hormones that are released into the blood stream during orgasm:
Endorphins - the body's natural pain killer. One of the most effective pain reliefs for a woman during her menstrual cycle is actually intercourse.
Phenetylamine - curbs your appetite: have sex, lose weight!
DHEA - a natural steroid that does a whole bunch of wonderful things for your body like improving your skin, cardiovascular, and immune system
Oxytocin (it's a neurotransmitter in the brain) - effects thing such as bonding and trust formation
The previous post was quite strong. I think that the emotional response to an orgasm might also be a part of the body's physiological response to it. At the time of an orgasm, the body experiences its own sensations, but there is also an emotional component, as well. To some extent, this emotional response helps the physiological one. Woody Allen once said, "We use the orgasm to make up for the shortcomings in life." I think that there might be something to that in terms of the emotional responses to an orgasm. If we think about it for a moment, an orgasm is a moment where some level of perfection or accomplishment has been reached. At this moment, it is as if there is a sense of complete understanding and totality. There might be a tendency to take this moment as reflective of so much. In the films, we see this. One person is coiled up with another, complete in both an emotional and physical sense of being "complete." It is this realm where we can see how the emotional and physiological responses to an orgasm merge, moving into one total experience. Another Woody Allen quote on this topic that might apply would be, "Sex without love is a meaningless experience, but as far as meaningless experiences go its pretty damn good." There is a convergence of physical and emotional modes of satisfaction and in both, the experience of consciousness after sex might lie.
Walking is a series of muscle contractions, as is throwing a baseball or chopping wood. An orgasm, however, is biologically much more than those, though I don't know that I would characterize it as an emotional response.
Besides the contractions, an orgasm also floods the pleasure centers of the brain, triggering euphoria and releasing endorphins and the chemicals oxytocin and prolactin. Both of these chemicals add to the feelings of calm and relaxation immediately following orgasm which, when mixed with the pleasurable feelings could be described as emotional response.
Normal series of muscular contractions do not affect the brain or trigger the same chemical release as it does with orgasms.