That's how I felt before dating my now-ex. I asked her to hangout on a Saturday night at a food festival thing and she said yes. I also put my arm around her when we watched our first movie together, and then kissed her after the second formal date. The kiss wasn't going to happen, but something (not booze lol) compelled me to just do it. Hopefully things work out better for you than they did me, but the unexpected confidence comes from nowhere and is like a high. The high is nice, but it can backfire too. The first time I told this same girl my feelings (months before we went out), I sent a message saying how I really liked her, and right after I sent it I was like "woah, where is this coming from". She didn't like me in that way at the time (apparently anyway).
I think you gain confidence when there's something you really want, it's like you lose sight of the possible negative consequences, and zero in on the positive.
Have fun