It has been natural for me to question and think deeply about things, including my salvation, and to doubt things, including my salvation. I think it has deepened my faith.
I think that thinkers will do this, and people who are more non-reflective will not.
I think if we just reaffirm our faith, that is good, and that will increase our faith.
When we relax and refocus on other things, I think the Holy Spirit assures our souls of our faith in Jesus and our consequent eternal salvation.
We are saved by believing in Jesus. And who is Jesus? He is the God-man who died for our sins on the cross, was buried, and rose again on the third day. If we believe in Jesus, in this Gospel, then we can know that we are saved and have eternal life.
Then, in order for us to enjoy close fellowship and communion with God, it is important that we read the Word, pray, meditate, live in His love, obey, forgive, confess sin, worship, engage in friendship with believers, and so forth.