Hey there. Incredibly down or not, concert or not, you have quit using. So just be done with it.
Heavy triggers suck. I've had a few lately. I felt resentful that I missed the fun, angry that everyone was going out drinking and just at a total loss.
I got through it. I can't relapse. It's not an option. You can throw buckets of suck at me for weeks or even months but i still do not use.
I don't know as much as people here who have years, I do not have their sobriety yet so I can't weigh in on whether you should go to this concert. I know when I feel shaky the thought of going to something triggering freaks me out and I get extremely emotional because even the smell of relapse is a disaster for me.
Keep in mind what you have to lose, here. If you can't go and stay sober you could lose it all and not be able to get back for months, years, or ever. Be careful.