I am glad to hear that you are back in the saddle.

(I am not a psychologist, but I've had my share of "issues". So I offer friendly advice, but don't take it as a diagnosis or something--I am not trained for that).

Since you have determined that your difficulties are not physical, they are most likely related to stress and as you say "the pressure [you] put on [your]self." The panic attack is a sign that you are facing some sort of psychological reaction here.

While I doubt you can do much physical damage by continuing to train, I think you need to focus on what is going on psychologically. Unless you do that, your body will not adapt--because it is not a matter of physical adaption. Rather, without negotiating the psychological side of all this, your body will continue to give you problems as it tries to express the stress you are experiencing.

I would suggest you seek some psychological advice--whether in the form of reading books on stress and panic attacks, attending "stress-management courses", or perhaps even a counsellor of some sort. If I recall correctly that you are a university student, you should see whether your university has some of those resources.

As to the bike riding, I would scale down your expectations. Don't try to ride hard, just ride for the pleasure of having the wind blow through your hair.

I wish you all the best,
Jamie