These points are gleaned from a Reformed Protestant text-book on theology. First, how to understand this matter of "omni"... [whatever].
"Only God is independent, immutable, immortal, and eternal. This
cannot be said of any creature. That is why most of these attributes
carry the negative prefix and we call them incommunicable attributes -
attributes that are not shared with us, even analogically. However,
because human beings are created in God's image, they do share other
attributes with God, analogically. Where we have attributes similar
(analogous) to God's, he is always qualitatively different and
greater. Therefore, these communicable attributes will often have
the "omni" (all) prefix attached to them.
Wisdom, knowledge, and power are predicated of human beings, yet God
is all-wise, omniscient, and sovereign. Our knowledge is always
piece-meal and partial. We learn this, now that; we never comprehend
every piece perfectly, much less the whole puzzle. God's knowledge is
different. First, he does not learn anything because his knowledge is
eternally perfect and comprehensive {Psalm 139:1-6 is cited along with
other scriptures} God does not depend o the world for his knowledge
any more than for his existence. No more than his omnipresence can
his omniscience be limited or circumscribed within boundaries."
(Pilgrim Theology, pp82-84, Michael Horton, Zondervan 2011)
This means that believers can only recognise (as did king David) that God is omnipresent, while we are not. We cannot explain nor understand it. We only come to realise it by God communicating something of that to believers, otherwise we wouldn't have a clue.
Further on, the author points out that what David said in Ps.139:7-10 also shows the omnipresence of the Spirit of God (p.93). I would add that the Son of God also shows his omnipresence (e.g. in Matthew 18:20 & John 20:24-27).
Of course, we can never be omnipresent, so this is an incommunicable attribute of Deity. We cannot even begin to understand it, yet when believers are born of the Spirit and have faith of Jesus Christ, their whole perception changes, for the better. There is nothing to fear, that God is everywhere present. It is awesomely wonderful and comforting. There is no idea of "colliding into God constantly", as you put it. Conversely, there is the sense of God being with us constantly. That is what David wrote about; that even if he wanted to flee from God's presence, he couldn't. He may well have wanted to flee for the year after his sin regarding Bathsheba - until he then repented of it, and knew restoration - but by the time he wrote Psalm 139 he was glorying in the wonder of God's omnipresence. He couldn't explain it, and neither can any of us. But whenever we sense God's presence, that brings us to worship.