Why do out bodies get random chills for 1 second?
* Sometimes the body needs a reset/check things are working. So it just sends a large impulse.
(that way you can also make sure blood but foremost *lymphatic* (fatty fluid between cells, not blood) gets circulation which is important for a number of reasons. (eg. the immune system between the cells))
* Sometimes when you relax, your old ape instinct kicks in and tells you not to fall off the tree. So you get a tiny panic, just so your very very old ancestors wouldn’t fall and the crushed by the ground.
(Not 100% relevant but, sometimes the body takes deep breaths/yawn to reset the respiratory system. You need to fill those lungs every once in a while)
Nerves are not exact wires like the electrical connections in a computer are. They are basically tubes with a mix of chemicals, hoping that the electricity gets through. Sometimes there is a glitch in the ratio of this chemistry. This causes a wave of electricity to rush through a part of them all at once. It is in some way like a reset is for computer, it clears the wrong information out, so your nerves there can work again correctly.
When similar thing happens in the wrong area (i.e.: inside the brain, not somewhere around the butt), person can get an epileptic seizure from it.