Why is this so debilitating!?

[Vasallus]

So I've been doing really well with my anxiety lately. Dieting, quit smoking, all that jazz. I feel good, sometimes I feel great. Yeah I have a few hurdles, but I'm overcoming them! It's the hurdles that come out of nowhere that make it so difficult, and I nearly broke down today.

I took my niece to this large canyon in the country near the city I live in. I used to go there as a kid, so I decided to take my mom and her there so she could see it (she's 4.) So we get there, and I've always been afraid of heights, so I linger back while my mom and niece go closer to the edge, and I automatically start thinking about them slipping and falling. I managed to calm myself down, drank some water, and my niece wanted to walk down the winding path that leads to the bottom of the canyon. I volunteered to take her while my mom rested.

Now, as a kid, you would never see me inside watching TV. I was born and raised in southern woods, mud puddles, and large dirt piles. Being surrounded by nature has always been my biggest comfort. So we start walking down the trail, and I feel fine. My niece is asking me a bunch of questions, and life is all good.

Then it smacks me out of nowhere. I feel a little out of breath from walking, and then I immediately think "What if I have a heart attack? What if I get bit by a snake and my mom can't hear me calling out for help? What if we get attacked by some wild animal?"

I ended up having to turn back and go back up the hill, at which point I got more out of breath, but it wasn't anything terrible. I workout occasionally so I'm used to it. I was kicking myself over the situation so much on the drive back. Not only did I feel like a disappointment to my niece because she really wanted to see the bottom of the canyon, but I felt like a huge failure to myself.

Why can't I do the things I used to? Why can't I behave like I used to? What, it's not enough to be afraid of something being wrong with my body, I'm afraid of nature itself now? I just...urgh.. sorry to rant. I just need some help here. I'm seeing a therapist, I'm meditating, I'm dieting and exercising. I'm doing EVERYTHING I can think of except medication to fix this, and yet I can't even walk down a nature trail without conjuring terrible thoughts of doom and gloom.

Someone help please.