I use to have just random episodes once or twice a year before i knew what it was. I always that it was just a spasm because it lasted a couple seconds. After i had my biggest episode at 250 bpm for 45 minutes i went in and was told i had svt. Ever since that episode they came more frequently but everyone is different. I would say its normal.
Mine occurred 3 to 5 times a month as I entered my 50's.