This phenomenon could be explained in simple physiological terms. Specifically, we need to make some references to the physiology of sexual response.
Our sexual behaviour could be broken up into four phases: excitement, plateau, orgasm and resolution. Not to get too technical and for the sake of brevity, the excitement stage is triggered by any of a variety of sexually arousing stimuli, e.g. getting on massageplanet.net in the search of a place to go, reading reviews, getting to a MP, seeing girls upon the arrival, etc. The excitement phase reaches its peak when the erect Mr. Cook cannot be ignored that easily (tip: girls, this IS the time when you start discussing other options, if you in Miss. area, where it's legal).
If the sexual stimulation continues with sufficient intensity (tip: girls, remember to gradually accelerate from 40 to 60-80 mph at this point), a peak level of vasocongestion is reached in the plateau phase, e.g. rate of breathing, pulse and blood pressure increase, but the cognitive and language faculties, from my research, decrease rapidly (tip: girls, this is THE time when you ask for the money! )
The arousal reaches the critical point (obviously for both parties involved with the gentleman's principle in mind i.e. 'Ladies first"; girls, make sure you counted the money, otherwise you will not reach this stage!) and double orgasms happen. Tip for the guys: in order to make your partner climax repeatedly and earn yourself a title of a studdd, keep on throwing some more, let say, monetary incentives at your partner at regular intervals at this point and you, and everybody else, WILL hear her screaming!).
Resolution phase. You come down from a natural high. Your physiological reactions are reversed, hence the lowering in the mood. Depression most likely to occur at this stage upon close examination of the wallet or flashing images of judging angry faces of people that might discover your hobby.