you are better seeing a cardiologist soon and make sure you mention your brothers death to him, sounds like he had sudden adult death syndrome but was never told as he may not have had tests or even symptoms.
this can happen in very healthy people too even well trained athletes especially if they never have symptoms so it cant be picked up.
panic attack symptoms can also be a sign of a thyroid problem so get ur thyroid checked through a blood test
sorry about the death of your brother i hope you get ur problems sorted you'll the be able to live life to the full again :)
It sounds like you might be due for a checkup. I would take this information to the doctor and get your information refreshed.