Can anaphylaxis stop suddenly? a couple of times after passing some bushes&plants i thought my chest&throat felt tight. once i got in my car i was ok?

It's not anaphylaxis: I suspect that you may have an allergic respiratory condition which is aggravated by passing through the bushes. The allergens then get airborne and caused the symptoms you described. You would have been much sicker and for much longer were the problem from anaphylaxis. You should consult an allergist.

Sometimes: During an allergic reaction, a person can release their own Adrenalin (epinephrine) and mild anaphylactic reactions can resolve. It is unlikely however, that a severe anaphylaxis would resolve spontaneously.