This is true in so many ways. And I've experienced 2 of the 3.
Depression is no joke. It is a serious mental illness that has such a stigma attached to it. In fact, I was probably guilty, at times, of not fully understanding how people feel who have depression. But, given that I have now experienced it, I can honestly say it is one of the worst feelings in the world. I can't even begin to describe what that hole feels like. There really are no words that do it justice. You just feel like you are constantly falling and there's no light at the end of the tunnel. It's so true that you live in the past when you are depressed. I know I did. All I could focus on was what had gone wrong in my past. How people had wronged me in so many ways (at least in my head) and how the past just "wasn't fair". I couldn't see beyond what had happened to me and I couldn't find a way to work through it. It was easy to just blame everything in life on the past. Especially the bad stuff. That's no way to live.
I've never experienced a clinical diagnosis of anxiety. Never had anxiety or panic attacks. But, I can see how those with anxiety live in the future. Much the same as those with depression issues live in the past. If you're constantly thinking about what is going to happen next, all you'll be able to think about is the future. You'll never be able to live in the moment. In some respects, I've seen pieces of this in myself. With my depression, I also had to plan everything out. I needed to know what was going to happen, how, when, etc. Some of that is just my personality. But, a majority of it was just my need to find control in some way, shape or form.
Often, that's the crux of anxiety and depression. Clearly, I am not an expert. But, speaking from personal experience, it's about finding control in your life. Without control you often feel that spiraling feeling I described earlier. And, it can be pretty scary at times.
So, now that I feel "at peace", is the last part of this quote true? 100%. I enjoy every day life. I live in the moment while being thankful for my past and planning for my future. Every day is an adventure. And I look forward to it. I'm so blessed that I get to wake up every day with a smile on my face (despite not being a morning person). My blessings are so plentiful I can't even begin to list them all. I think about where I was 2 years ago and I don't even recognize that person. Words can't describe the change that has happened in my life over the last two years. Lucky and Blessed hardly do justice to what I've experienced. And life just keeps going and gets better all the time.