What does "gut instinct" mean?!

What does "gut instinct" mean?

It is sort of indescribable,
but there is another word for it... your intuition.
It`s something you feel inside you, mainly in your stomach or your chest, the physical part of your conscious.
It tells you what to do, but mainly what not to do.
It`s the part of you that keeps fighting against something.
It`s kind of like hesitation, but a stronger feeling.

For example you`re about to go on a really big roller coaster, with corkscrews, loops, drops, and backwards - you know, the works. However you are not mainly a big roller coaster person, but your friends are urging you to go on with them. So, there`s this little feeling inside you saying "No" or your palms start to sweat, your head starts to pound, etc.
You ignore the feelings and go on the ride. And right before the big drop, you think, "CRAP. I should have gone with my gut instinct."

Same thing as choosing not to walk through the dark alleyway at 11:00 pm because of feelings that something bad will happen.