What Causes Increased Heart Beats And Panic Attack?

Hi, just the other day I had a serious panic attack. I went into the emergency and they said it was nothing. Before the panic attack ocurred I had drank a Nos energy drink. I am wondering if that was part of the cause because when it happened I was browsing the internet doing absolutely nothing and it came out of nowhere. So I thought maybe alittle jog outside would help, I jogged for literally 15 seconds before I started breathing very heavily, I a an athletic person this doesnt usually happen to me, but what I am really concerned about right now if that just a moment ago I was doing wonderful ready to sleep nothing affecting me, but as I was laying there I started to shake randomly and my heart started beating really fast on its own, and i'm scared to lay down now.