It is quite right that you should feel that “something terrific” has happened to you (It has) and be “all glowy.” Accept these sensations with thankfulness as birthday cards from God, but remember that they are only greetings, not the real gift. I mean, it is not the sensations that are the real thing. The real thing is the gift of the Holy Spirit which can’t usually be—perhaps not ever—experienced as a sensation or emotion. The sensations are merely the response of your nervous system. Don’t depend on them. Otherwise when they go and you are once more emotionally flat (as you certainly will be quite soon), you might think that the real thing had gone too. But it won’t. It will be there when you can’t feel it. May even be most operative when you can feel it least.
If we have shared in Christ’s death and Resurrection through Baptism, and especially if we have received Confirmation, then we can and should be confident that God is always with us. Of course, we can choose to turn our back on Him through serious sin. But once we repent and turn back towards Him – going to Confession if needed – then we must trust in the promises of our Lord who said He would be with us always. And this remains true even if we do not “feel” His presence. Lewis is very right here and we would do well to reflect upon his words especially when we do not “feel” God.