Throughout my whole life I have heard people expressing about how they had a religious experience. One of my mentors once told me how he was walking close to the coast and he was awed by the beauty and he felt something inexplicable in his chest and that is how he "knew" god existed, others have different experiences but they all, in their own way, describe almost the same feeling. You also hear about people that have had a troubled life and the first time they walk into a church they are filled with the spirit of god.
I have many times pondered on this and have come to this realization, just like the feeling of being in love has been romanticized into a magical force, but science has since discovered that those feelings are simple chemical reactions.
I have copied and pasted this from http://www.healthtips.in/love-heart-body.asp you can find more info if you go to that website.
The first spark comes from the brain that releases a neuro-transmitter chemical called dopamine. This results in a chain reaction leading to the heart pounding three times faster than normal. The extra gush of blood finds its way to the cheeks and sexual organs. This sudden diversion of blood makes your stomach feel a bit empty and this causes the feeling of butterflies in the stomach. Since the blood goes to specified areas, the hands and legs get a diminished supply of blood resulting in the palms getting cold and a slight shiver setting in. This is why many in love look a bit disoriented, nervous and they wear a new colour on their face.
You also have different causes for effects like this, for example: Vertigo - a dizzying sensation of tilting within stable surroundings or of being in tilting or spinning surroundings.
There is also the feeling that someone that has been in hostile captivity for a period of time and one day somebody comes to the rescue, they think the world of their liberator, and feelings erupt like a volcano.
Some people live their lives in agony for many reasons, they feel unloved, go through life feeling like the whole world is against them, one day they walk into a church and they are struck by the IMAGE of a place where everyone loves each other, everybody treats them well and bam!!! they get that feeling that they've never felt before and cannot explain... enter the priest, and the priest tells that person "that sensation you are feeling is the spirit of GOD coming into you" ... after that how can you ever convince that person that God does not exist? and even if you could, would the person even WANT to believe you? when realizing that god does not exist would mean going back to a life of suffering.
So there it is, that is my explanation of the religious experience, if you have a convincing argument against what I just wrote I would love to read it.