What do you do when you get that heavy feeling in your chest...of feeling unsettled and almost a little panicked?

Anxiety or a panic attack. The best thing to do is acknowledge it and ride it out. The more you try to handle it the more often it will happen and it gets worse.
Its a horrible thing to go through but billions of people experience it all over the world. We just have to acknowledge our feelings, positive & negative and hope you don't do anything stupid before its over