It is quite possible to find the negation of belief in God itself be a spiritual/freeing experience, especially if this follows prior subjugation/belief in an organized religion. Relinquishing religion can itself be a "spiritual" experience precisely because of how shitty religions tend to be.

Also, many mathematicians find a spiritual purity in certain equations and proofs. There need not be anything religious about such an experience. Something can be "deep", completely devoid of the paranormal.