It could be something subconscious. Could be last time you heard a particular song or radio announcer you were having an anxious day--or an adrenaline filled day. perhaps months later even though you've forgotten about it, it's there in the subconscious and your body has the trigger again. Heck, sometimes I get a surge of nervousness when someone compliments me. no good reason for it, but it happens.
My point is that sometimes there isn't a good reason for bodily responses....be they anxiety-driven adrenaline surges or adrenaline surges that aren't anxiety. Now if you were to have these surges daily, for extended periods of time, and were having chest pains, headaches, blood pressure spikes, then yes that's something that needs to be addressed.
But our bodies, as people with anxiety disorders. are sensitized to stimulation. People without anxiety likely have similar adrenaline surges at seemingly innocuous things. (from caffeine, medication, sugar, subconscious memories....or no good reason at all). Someone else may brush it off and not give it much thought. Where with anxiety, we try to analyze and pick it apart for....and then perhaps start to dread these otherwise harmless blips in our day