The derealization sensation you describe is a form of an anxiety attack. Sort of a mental confusion combined with a common anxiety attack. You might call it a PCS anxiety attack.

It is a sign that you should remove yourself from the environment. Get to a quiet area and sit with your eyes closed. This may help your brain regain focus. Take you pulse and BP if possible. They are probably elevated.

When you get the chills, try sucking on a spoonful of honey or sugar. If it helps, you blood glucose may be low. Your body will respond quickly to sugar from the honey that is absorbed sub-lingually (under the tongue).

If this reduces the chills, try consuming a low glycemic snack.