Trying to see if I have a case

You have a case if there is medical opinion or reason (i.e. the opinion or judgment of other doctors) to think that you were misdiagnoses *and* that the misdiagnosis harmed you. Not only do you need to have both things, but as stated, they need to be supported by sound medical opinion. In terms of misdiagnosis: other doctors would have to feel that based on the symptoms you had, that the hospital should have done tests or followed up more; if the average reasonable doctor would have felt that this was a panic attack, nothing wrong was done, since doctors are not required or expected to be perfect--just to do what the current medical standards call for in terms of test, treatments, etc.
In terms of the injury, you have to show that if there was a misdiagnosis, that it harmed you some way--for example, made the effects or prognosis of your stroke worse. If you would have been in the same condition or had the same outcome even if they had tested for a stroke immediately, the misdiagnosis did not cause you any harm and so there is nothing to sue over.
So what you need first is to get a sense from other medical professionals as to whether they should have tested you when you first showed up and, if so, whether that would have changed the outcome. Once you know that, you know whether you have a case or not.