Can u have severe allergic rxn (full body hives, red swollen cheeks, congested) from possible cross contamination w/ tree nut u've never eaten??

Possible: And probably you were previously exposed without knowing, or you happen to be allergic to something that cross-reacts with the same nut in suspicion. At times you can have the reaction without any stimulus. At any rate, given your history, it's worth keeping epinephrine pen and antihistamines handy, and see an allergist, check aaaai.org or acaai.org for an allergist in your area, good luck