How open is too open?

Been pondering - can you be so open to the Holy Spirit that you inadvertently let all sorts of unwanted spirits in?

Let's say you've been erring on the side of conservatism, and are skeptical of anything too "spirited". One day you get a glimpse of Spirit-filling, and open the door a crack to let the Spirit work. It goes pretty well, so you decide to be completely open from now on, and see all sorts of things happening in your life. You get more and more "spirit-filled" as time goes on, opening that heart-door more and more, absorbing what comes along ... but suddenly the heart-door is so open that you absorb ANYTHING that comes along! God-spirit or otherwise, perhaps you lose the ability to tell the difference between what's purely God and what's a bit on the suspect side, emotion-driven or leader-initiated perhaps.

Possible? Can one be too open? It is perhaps better to be a little reluctant, to test things before absorbing them or letting your emotions / the leader carry you off?

I ask because I've seen things happen in a certain church (which scared the heck out of me) that were "a" spirit at work, but not God's! Those who were all for it and completely involved were taken over, but those who sat skeptically felt a dark spirit at work that had nothing to do with God. It seemed pretty easy to be confused... these were church-going folk who really got into things when the service heated up. The line between light and dark was very misty.

Maybe that's why I'm not as open to spirit-manifestations as I could be. I don't feel I yet have the strength in God to discern what's right and what's not.

Thoughts?