It is a painless experience.

Preparation to birth is more frightening than the actual eventuality. Because the soul which is residing inside the body hesitates to leave the body as it has developed a deep attachment towards the body. Moreover, the soul looses its ability to recognize itself. Its cognitive ability is limited. It just can't realize the power beyond the body. So there is a friction or a creation of fear about leaving the body.

In fact, soul departure from the body is just like removing an old shirt and wearing a new one. Even the modern science admits that energy can neither be created nor can be destroyed.