When I was young, I could hadve been about 12 years old, I usually did relaxing sessions listening to a recording.

I remember how I was relaxing several body parts, beginning in my feet and ending on themy head.

Always I had a good level of relaxation.

you could also say "I was always well relaxed"

But once, occured someething unexpected happened.

your word order is unnatural here

I was enjoying of the relaxing when suddenly I noted how as came out ofrom my body.

Some seconds later, I noted how I was levittating to close to the ceiling.

All this was very speedfast and strange.

very speed is not a phrase used, high speed is fast and low speed is slow. You could say "at very high speed" also

In that moment, I only wanted aone thing, this was to go back to my body, and a second later, I had wentwas back.

All seemed ok, and like this way, this experience ended here.

When I was young, I could had about 12 years old, I usually did relaxing sessionsoften relaxed while listening to a recording.

Perhaps by relaxing sessions you mean meditating? In which case "I often meditated while listening to a recording".

I remember how I wasould relaxing several body parts, begining in my feet and ending on themy head.

AlI ways I had a good level ofalways very relaxed.

But once, occured someething unexpected occurred.

I was enjoying of the relaxing when suddenly I noticed how asthat I had caome out ofrom my body.

Some seconds later, I noted howthat I was levittating to close to the ceiling.

All this was very speedudden and strange.

In that moment, I only wanted aone thing, this was to go back to my body, and a second later, I had went back.