I had my first at 19, not that long ago either, scared the ******** out of me, was alone in the kitchen with most of the lights in the house off, tired as hell and stressed over relationship stuff.
Suddenly I felt this incredible sense of doom, felt like something was above me, around me, no idea what it was, I was thinking logically going "there isnt anything there" but my heart was going a mission miles an hour, sucked big time, had a minor one when I was at work in the office alone but that passed as soon as I got outside.
Found out we have a family history of it which is never good to hear, getting off the smokes sounds like a good plan though. Interesting to hear about other peoples stories as well