This reminds me of how, when I was young, I used to walk the tops of walls when framing houses. No problem. Then one day the fear of falling set it. I started to try and talk myself into it, telling myself I've done this hundreds of times, but as I started to move, my legs began to shake, and I realized if I tried to push myself through this fear, I'd probably fall. So that day I stopped walking walls.
If I decide to perform again, I'll start with open mics, and I had already thought that I'd do what Bleujazz suggested, and just go check out the scene a few times first.
But if I ever gig again, I'm not approaching it from an improv setting, like jamming with unfamiliar musicians at an open mic. I would just do that as a stepping stone to getting back in front of an audience in a cover band. So I do agree that preparation and having that muscle memory take over for you are key to minimizing the nervousness, that I'm sure will always be there. I just need to get back into that comfort zone, that certainly includes some anxiety, but it's derived from excitement, not fear.