If you have recently been seen by a cardiologist and had a thorough work-up, then your next big hurdle is to accept his DX that your heart is just fine. If you don't trust this, then by all means, go for a second opinion, but if the results come back the same, it's then time to get in front of a therapist to deal with the anxiety behind the "heart" problem. Many of us with anxiety/panic issues focus on our hearts, which is called Heart Anxiety and it can become a very vicious cycle. We feel our hearts "doing" something we perceive as abnormal and then we start the anxiety which in turn WILL affect our hearts which then gives us even more reason to believe it was our heart in the first place then the anxiety soon becomes panic and our heart reacts to the dump of adrenaline like it's suppose to by beating harder and faster and then we KNOW we're having a heart attack so we then start to sweat and our fingers get numb and then we feel pain in our chest and our heart gets even more wonky and...................it's a merry-go-round from hell and you need to get off.
If these "attacks" are transient, not lasting more than a few minutes, even if they happen every day, I don't believe your heart is in any danger whatsoever, it is one of the strongest muscles in the human body and can withstand a massive amount of stress before it reaches the "red line." Your cardiologist would have picked up on any damage and hopefull you told him in detail what you feel during these attacks. Feeling tired after one of these attacks is very common and quite normal. It's one of the side effects of the adrenaline........a hormone our body dumps into our system when the "fight or flight" light goes on. Since we do not have to fight anything or flee from anthing, that adrenaline still does it's job by preparing our bodies for either of those options. When the feeling passes and we calm down, our body reacts by sort of slumping into "I need a nap mode."
In my humble opinion, I think you have some anxiety issues and you would benefit greatly with some talk therapy and perhaps a SHORT COURSE OF A MILD anti-anxiety med.........just while you get this under control.
You might want to jump over to the Heart Forum and get some great feedback from folks who will know and understand your heart concerns even better than us. Can't hurt.
Let us know how you're doing, OK?