I would suggest to the OP that the Spiritual manifestation is not something we should "Seek" in the sense of going to the altar hoping to be "slain in the Spirit" or whatever.
There are several cases of this manifestation recorded in the Bible.
1 involving Abraham
1 involving Daniel
1 Involving Peter
1 or 2 involving John
Possibly some with Paul
I've had it happen to me several times, and I can tell you that There is no need for anyone to catch you.
I suppose they may as well catch you if they are standing by, but the Spirit of God isn't going to do this to you and let you get hurt anyway.
I once fell across a Pew, right across the middle of my back, and wasn't hurt at all. Nobody caught me.
So when it really is the Holy Spirit, nobody is going to get hurt, and in all likelihood someone will be healed in some fashion, or born again, or perhaps Baptized with the Holy Spirit with tongues for the first time..
This one time I was praying, standing at the altar during an altar call, and I don't know how to explain it, but the Holy Spirit put it in my heart to just let go and fall back. Nobody was praying for me specificly, or even for anyone standing near me, as far as I know.
When I fell back I hit the person behind me, who apparantly tried to catch me, as far as I can tell, and instead they fell out slain in the Spirit. I've never quite had something like this happen before or since, and it took a bit of trust just to do it.
It's different every time, but its the same Holy Spirit, or at least, as long as it is of the the Spirit then it is obviously good and in God's graces.
Still we should not necessarily actively seek this, unless you really feel led to do so by the Holy Spirit.
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How to describe what it "feels" like.
Well, it is like floating in space sort of feeling, very peacful and calm. Usually, you remain partially conscious and you're aware of things around you, but not really concerned with earthly things while its happening, because usually it is deep in prayer, tears of pure joy, the love and mercy of God permeating your body and spirit.
It seems to happen in varying degrees. Ranging from complete unconsciousness where you scarcely remember how you got there, to just barely a weakness where you don't even fall over.
Also, the length of time can vary from just a few seconds, to perhaps several hours, which I suppose would be like Peter's "Trance" recorded in Acts.
When it happens to me, I can usually speak and continue to pray, praise, sing or whatever it is that I'm doing, but my other members seem to go to sleep. LIke I said, floating in space sort of feeling, and you don't want it to end.
You can open your eyes if you want, and you can force yourself to move if you want, but I find that is best if you just surrender all and let the Holy Spirit heal you or speak to you, or whatever it is he's doing.
Anyway, I hope this isn't too lengthy, I have sort of a habit of making very lengthy posts on forums.
Just remember, if you ask for bread, Jesus is going to give you bread. If you ask for water, you get water, and if you ask for fish, you get fish.
God gives good gifts to his children.
