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Not to get medical but pleasure comes from two very specific chemicals being relesed in the brain. Studies on this have proven that women can create huge amounts and over stimulate, meaning the areas of the brain that were the inteded recipients are so flooded that it literally spills over to other parts. Hence, a touch on the arm causes triggers in the brain to open the corresponding area to produce tactile touch, but instead is flooded by these pleasure chemicals creating another orgasim.
Two issues or as we call it defeses that the brain has.
1 - it is able to sense an over flow and so it starts to naturally 'drain' for lack of a better word itself, a self preservation mechanism that we understand very well.
2 - there are only very specific states in which an over flow can happen, hence the Tantric teachings trying to get the body to respond in specific ways. Specific conditions must be meet in order for an over flow to even have a chance of happening.
Can an over flow happen? Yes.
Does it happen to everyone? No.
Can it last for 30 minutes or longer. Yes but that is exceptionally rare as the brain's natural defense starts to work once it is detected. 2-5 minutes is considered a long time in any over flow event.
Are there differences in the brain that allow certain women to experience this while other women cannot. Yes, each brain is unique therefore some women can produce more while some women have a hard time producing any.
Always remember the brain is the strongest sexual organ you have.