Speaking in tongues is speaking to God, not the enemy. Don't believe that guy.
As far as your experience. If you felt peace and still do, look at the fruit of it. He is the King of Peace and His Kingdom is this...
Romans 14:17 For the kingdom of God is not a matter of eating and drinking but of righteousness and
peace and joy in the Holy Spirit.
I have experienced things like you, I have been "slain in the Spirit" and fell to the ground before I even knew someone was behind me to catch me, another time I fell back and so did my entire row. The fruit of this? I felt love like I hadn't before, peace like I hadn't, fear and night terrors that kept me awake no longer attacked me as much... I also started to hear from God more clearly.
People want to put God in a box, but He is radical. Pentecost wasn't a collection of people playing harp music and speaking in order. Lol. It was a radical display of God speaking through people, including the miracle of everyone hearing their own language.
Don't be afraid, look for love, and you will find God. He is love. Also be careful of people who while well intentioned can be stuck in traditions like the Pharisees when they accused Jesus of casting out demons by the power of the enemy.
We are called to be in unity, not slander, not create division, and to love one another. That's how you know is a Christian according to Jesus. And we are called to share the Kingdom of God.

You experienced it. Now, go share it.
Matt 24:14 And this gospel of the kingdom will be preached in the whole world as a testimony to all nations, and then the end will come.
C.