Hi, I'm new, but I hope my story may help you.
Much like you, I never had any trouble with worry/anxiety in my 20s. For me, it all started with a divorce and some health issues at around 30 years old. (I've been a Christian since I was 9).
You're not alone. About 2 years ago, I had what people told me was a panic attack in traffic. I had to pull off the interstate to a gas station. I was shaking so badly that I could hardly talk. It took a few hours for me to calm back down. At the time, I thought it was a medical issue and that further made me panic. I had to call my husband who came to pick me up. I thought I even needed to go to the ER, but after a quick call to my doctor, he said that I had all the classic symptoms of a panic attack. I took a couple weeks off from driving and then just forced myself to get out there again.
It's been two years since that happened. In the beginning, I kept Christian music in the car and listened to that as I drove (and sang along with it). I think singing out loud to God really helped, too. If you haven't tried that, I'd suggest trying the Christian music and praying or singing aloud.
Gee, I sure hope this helps you. I have had quite a bit of relief from anxiety of the past couple of years. So, if I can ever help give ideas, just let me know.
I haven't used any meds (I think there's nothing wrong with them, though) or anything herbal, etc. Really, it's been prayer, casting all cares to Jesus and keeping my thoughts focused on other things. Sunflower2007 suggests something very powerful: focusing on other people. I find that when I'm serving others in Jesus' name, my stress and anxiety goes down.
Memorizing certain scripture verses has helped, too. Sunflower2007 provided some really good scriptures above. Maybe committing those to memory might help (or printing them out and keeping them with you.) One of my favorite verses is Proverbs 3:5 (and verse 6).
I also have started taking B Complex after finding out through a blood test that I had a B12 deficiency. I have since found out that a B12 deficiency can cause all sorts of anxiety-like symptoms, so you may want to have that checked.
Have you been beating yourself up over this? I know I've spent plenty of time beating myself up over being anxious--feeling like I was terribly lacking in faith. Try not to do that. Just continue to pray for God's strength and for healing.
Also, pray for God to reveal to you the root cause of your anxiety. That has really helped me. Even though I'm a Christian, much of my anxiety has been related to illness. In the end, I realized that I was scared of dying. I'm sure a lot of people would say that it's silly to be scared of dying if you're a Christian. But, regardless of what my brain my think (I know I'm going to Heaven because Jesus died for me), my spirit sometimes gets weak and freaks out.
I hope you get some relief soon. I'll say a prayer for you. May God bless you and give you complete peace in your spirit. May He guide and direct you all of your days.
Love in Christ,
Ephesians4