When the Spirit confirms truth to me, I literally get a physical sensation to affirm the insight, almost like a shiver/tingles feeling. It's unique and unmistakable, and it's unpredictable with a rapid onset. I have experienced this phenomena since I was 21 years old, that's the earliest age I noted the feeling. I noticed after awhile that I could really trust it. It was the only confirmation that was 100% dependable. Anytime I was pondering the truth of some philosophical or technical issue, if that feeling corresponded with something I was thinking about I knew I was on the right path. I tested it repeatedly, and it always proved true. I couldn't find any verifiable instance when it failed! Which is almost unheard of in science. It was like a cool trick or special power, a benevolent confirmation I knew I could count on though I wasn't sure the nature of it. I assumed it was some neuronal phenomena where synaptic connections generated a physical sensation from properly integrated data in the brain, or something scientific like that.

I was mostly thinking about the big questions of the universe back then, and my school major was nuclear biophysics because I thought it would help me answer these burning questions. (yes, I was a big nerd, lol) I minored in chemistry too, so I was very science minded. It wasn't until God found me at 27yo that I realized that "feeling" was the Spirit all this time, and I just didn't have the Biblical background to ever consider it. The Bible was the last place I thought I'd ever find the answers!
But what is so interesting to me, is that He gave me the Spirit even before I believed! The Bible says we are saved by grace through faith, but in my personal experience,
it's practically all grace. My faith was zero when He saved me. The grace component is profound with Christ. Perhaps He anticipates our eventual faith, and gives it forward? I just know I am extremely humbled by it all, looking back at all the messes He saved me from. This gift of Spirit is real, and available to ALL men (believer and unbeliever) as long as you sincerely seek truth. He rewards those that diligently seek Him, but you must be a seeker to find it.