When I started tweaking my training style I began to experience something akin to what you're describing. I was on a treadmill, and I remembered being almost scared by the fact that I was bumping up the incline and speed and it wan't making me tired. I still manage to get that "feeling" at least once a week if I can help it.

Back when I played handball, I read an old book that mentioned how athletes tended to find a certain "flow". I guess what I experienced was similar to that, but only in terms of cardio. In the very least, it makes you question a lot of your perceptions about training and personal ability.

I stumbled across this awhile back, and it summed up pretty much everything in tri and my personal life in one shot:

"...Our deepest fear is not that we are inadequate.
Our deepest fear is that we are powerful beyond measure.
It is our light, not our darkness that most frightens us.
We ask ourselves, Who am I to be brilliant, gorgeous, talented, fabulous?
Actually, who are you not to be?
You are a child of God.
Your playing small does not serve the world.
There is nothing enlightened about shrinking so that other people won't feel insecure around you.
We are all meant to shine, as children do.
We were born to make manifest the glory of God that is within us.
It's not just in some of us; it's in everyone.
And as we let our own light shine, we unconsciously give other people permission to do the same.
As we are liberated from our own fear, our presence automatically liberates others."

'A Return To Love' (1992) by Marianne Williamson

Back in high school PRed in the 3k on the track by almost 25 seconds one day out of the blue. I had run the entire season finishing in about the same time each race, and then in the last race of the season had a breakthrough of 25 seconds. But it felt easy the whole time.

I knew I was gunning it, but had no idea it was so fast. Just felt smooth and fast the whole way. Not effortless exactly, but never straining and never feeling like I was slowing. Was pretty cool.

Haven't felt good on a run in the last ten years though!

Weirdest zone experience I had was in college, during a taekwondo tournament which took place in my home town. My girlfriend was there, so were my mom and a sister, and I was surrounded by friends. I was contented, relaxed, happy---all rare for me at the time.

I half-assed my way through a point style match and lost without giving a damn at all, just uncommitted and unconcerned because I was setting my full attention on the Olympic style fights ---back in the day where "trembling shock" was required to score a point---for later that evening.

First fight was against a friend who was faster, stronger, and meaner than me, and I had a pretty good idea how he'd open up the fight, so I just rehearsed what I'd do: block the chippy push kick he'd use trying to get me moving backwards, and then I'd punch him really hard.

Right off the bat, it worked. Blocked his right leg with a low block, and then punched him with full force right in the solar plexus, which was completely exposed. Exchanged a couple short kicks, clinched, repeated. He just couldn't stop trying that move and I started really coming out of that punch fast as I could, kicking hard regardless of whether he was trying to chase or move back. I could tell exactly what he was going to do way ahead of time and I started hearing voices telling me what to do next. Even when he tried different things I felt equally as confident as I had in those first couple seconds. Auditory hallucinations kept pouring In, predicting everything that was going on. I kicked him in the head hard a couple times, and just watched him fatigue, bewildered. In the last round he came at me with a couple attempts to knock me out, but we both knew it was over. I too was bewildered.

I looked around. Everyone in the vicinity of the ring who knew us both really well looked just as bewildered as us.

Never fought that well any other time. Going into that fight we both knew he was the better fighter. But I'd shed my fear of losing by ditching the point style match. He was over confident, and apparently I was batshit crazy for three rounds.

My next fight was against my original instructor when I was a white belt. No auditory hallucinations for that fight. Not to say it was as easy, because he'd seen what took place before and came out with a big mix of tricks, swinging for the fences, and when those didn't land I just waded in with counters.

Ended up winning that tourney.

Never really heard voices again.