I developed some issues with anxiety that I've been working on, and perhaps my experience can help you. One of the things I got anxious about is riding my bike even though I also love it.

It's critical to desensitize yourself to what makes you anxious, and that the only way to do that is to expose yourself to it whether you want to or not. Easier said then done… But I've found that planning in advance works best for me. I'll put something on my calendar, internalize that it needs to happen, and let inertia carry me through into doing it. It's even better if I plan something with my husband, because he will make me go no matter how miserable I am about it.

Another lesson I'm working on internalizing is that motivation doesn't matter. You don't have to be motivated to do something, you do it because you have to and/or learn to anticipate the accomplishment of having done it. For you, maybe wanting that feeling of exhilaration that you described instead of wanting to actually ride your bike could get you going. Doing something major isn't even necessary to get that pattern of behavior started; going to the park and riding on the flat trail is an excellent thing to do!

Finally, if you've been off the bike for a long time you might benefit from adult skills classes (example), or by checking out some group rides in your area that are aimed at new/slow/recreational cyclists. I found this in Sydney, maybe they could help you get started?

Good luck! Keep in mind that time and practice will really help.