Okay, wow, yes, you sure do sound like you have a lot of anxiety about this!
First off, doctors do not dismiss patients because they cry or have panic attacks. People with anxiety have as many real health problems as the non-anxious, so even if your doctors SEEM dismissive, it's not because you have GAD, it's because they don't believe there's anything wrong with you that warrant follow-up tests.
At this point, honestly, who cares if what you're feeling is from the bump on the head or your anxiety? You bumped your head three weeks ago—it's time to think logically about this. If it was something truly serious, that would have been apparent by now. I get it, I know how you feel; I used to deal with awful anxiety, too, and have an over-active imagination, but at a certain point, it becomes UP TO YOU to talk yourself off the ledge. From your post, you're already doing this to some extent, countering your more anxious thoughts with more logical ones. That's good, but in order for you get a true handle on your anxiety, you're going to have to take it one step further by also refraining from seeking reassurance or getting tests you don't need. Your doctor thinks giving you a CT scan will calm your fears? Clearly, she doesn't know how HA actually works. Sure, it may give you peace of mind in the moment, but without addressing the anxiety, you're soon going to doubt the outcome of the test or jump to the next health concern—unfortunately, that's how our minds work.
If anxiety is an ongoing issue for you, I'd recommend getting some professional help. Counseling and CBT are excellent resources. So is medication, and I bet that if you KEPT taking Prozac, and allowed yourself to put up with the unpleasant initial side effects, you'd find that it would help alleviate your more extreme jitteriness and allow you to see things more rationally. Taking it now doesn't mean you'd have to take it forever.