You have to start somewhere, right?

[sundial]

Did I mention I have terrible depth perecption?

That can certainly account for your anxiety on the mtb. People who don't have depth perception deficits have no idea what it's like for someone who does. It can set someone up for panic attacks in crowded places. Technical trails are even more so to one who can't judge distance. I imagine whizzing in and around trees can be very nerve wracking as well.

Perhaps you can scout out a dirt packed trail that is open to ATV's and horses. These trails are usually wider and in some cases are not very technical. I like to ride on hiking trails in the state parks. Fireroads may be your best friend too as you have fewer obstacles to navigate.

You can always use your mtb on the street to exercise the dogs like I do.