Hi rottdane,
I am not an MD but I have never read anywhere of anyone having had a heart attack from a panic attack.
If you have had yourself checked out by a Doc and had tests done and been told your heart is ok and that its just anxiety/panic then you are afraid of the feelings you are having.
Just your fear of anything being wrong with your heart, a skipped beat, palpitation, slow beat, sharp pain, whatever the feeling that triggers your fear is enough to keep you in a sensitized state.
Sensitization,Bewilderment and fear keeps the panic cycle alive.
Understanding and retraining your reactions to these feelings is what you need to work on.
I am certain all of us here have had extreme panic attacks at one time or another. Of all the people posting on these boards noone has died from panic!
Night time panic is very terrifying because you are woke up in the middle of the night already experiencing these horrible symptoms. But they are JUST feelings and fear, it is your fear of them that is feeding them and keeping them alive.
It will take time and patience to unravel the changes that panic and anxiety have brought into your life. I hope you are getting therapy, and following your Docs advise. But the main part of getting past all this is to change the way you feel and react to the feelings.
You might like to read "Hope and Help For Your Nerves" by Claire Weekes, she explains everything so you can understand what is happening.
Take care.