I have the exact same problem - but I can have symptoms for days!

I dont have an answer, but I think the symptoms is upper-neck or brainstem related.

I have had some big and a lot om small impacs, and it takes less and less to get symptoms (and obviously hitting a foam pillow lightly can not give a concussion), so my best guess is, that my nervous system reacts when something happens, which reminds it of the original injury, perhaps because my deep-upper
-neck muscles is not working properly, so my nervous system is in a constant fight or flight mode.

But just a guess....