Anxiety is it genetic or a learned behavior?

I'm trying to figure something out for my personal benefit.  See, some
people believe that anxiety is a learned response- that is, when they
are confronted with a situation that is stressfull they learn that
danger is attached with it. Others believe that it is genetic. I think
it is a combination of both.  Here's an example I am going to use for
this discussion...Johnny is a college student. Johnny attends lecture
on a regular basis when one day he is sitting in lecture when suddenly
he is panic stricken- What if I can't escape this lecture very easily?
What if i get up to leave when suddenly i trip and fall on my face.
Everyone will laugh" So johhny starts to sweat- breathing is
increased- he is experiencing anxiety. The next time Johhny attends
that class, he is confronted with the fear that the same thing is
going to happen.
    Now a person that believes anxiety is a learned response will say
something like this... "Lil ol johhny was never taught the right way
to react in a situation like this- he learned to be a negative
thinker, instead he should replace those negative thoughts with
postive ones." kind of along those lines. Fine- they are trying to
replace a learned response, negative thinking, with a positive
response such as "I will be fine. Everything will be ok."  Or, take
for example, the latest pyschological craze, cognitive behavioral
therapy.  This therapist would say something like this: (again based,
in my opinion, off of the learned behavior argument)"Johhny should go
to class even though he has this fear he won't be able to escape, and
eventually he will learn that there is no danger involved." I have to
admit it is a good way for Johhny to cope with the situation.
   Here's where I get lost.  Why the hell did that thought pop into
Johnny's head anyway? He was doing fine through college lectures why
did it happen so suddenly? This can be tried to explain through the
past and learned response. I just don't buy it. I believe that it is
genetic or due to a chemical imbalance.  I've read numerous books on
ways to treat anxiety disorders and 95% of them claimed that anxiety
is a learned response. If it was truly a learned response, then it
should be fairly easily unlearned. If the individual does unlearn that
response then good for him/her. but I can almost assure you that the
individual will have another "random thought" that will frighten the
him/her and then that individual will again be faced with the "tug of
war" to unlearn that random thought. And so on...I will say that I'm
thankful that they learned a way to cope with it.
   So, they learn to unlearn- in other words to cope with the
situation. I don't know- I've done enough rambling for one night- what
are your thoughts on this? Is anxiety a genetically generated
condition that improves with coping skills? Or is it a learned
behavior that can be corrected with new thinking ways?  More study is
greatly needed on this to help with medicine decisions.