I am a calm person, it is highly rare of me to get angry to the point of seeing "red" to get that form of adrenalin, i might keep my self from doing this becouse i know the angry kind of adrenlin makes you lose your control over youself
Now i have never been in a fighting situation to where i did not feel that i had a good amount of control over it at lest in the ones that actually ending in a fight, i allways try to keep my self calm and to where i think adrenalin can go two ways, it can do into a controlled form and a beserker form, a berserker form is like when some one is so pissed they loss all self control and generaly start swinging, this is bad if the MA is doing this becouse all is techniuqes are all ou the window, i think this is good for a MA to get the oppinit to be come "Beserk" becouse then his attacks can become obviouse but sence he is fuled with adreniline, if he hits you chances are he will hit you really hard

Now the controlled one is what a focused MA or a focused anyone will get to
it is where it isnt channled to anger and power but become more of a defence type, at lest thats what it does with me, to where it felt like i could take any hit without hurting, know dont get me wrong, it hurted a lot after the fight but wail in the fight i felt like and did take hits without flenticing
Now like i said that is when i felt like i had a good amount of control in the situation, now (before i started MA) sometimes for whatever reason at school or wherever some one will come up to you pissed off about something out of know where and thus catches me off guard meaning that i have little or no control over the situation, and thats where i would feel the Flight or Fight feeling, now generaly i feel that shaking feeling you mentioned and my general goal(like i said before i was a MA) would be to defuse it, find out why he is pissed and try to take some control that way, see why he is pissed and find a way to fix it, most of the time that works, usally becouse they dont want to fight unless provokes and sence i tryed to find out the cause and solve it i havnt yet(in the situation that i can remeber) been in a fight like that, i but i would remeber feeling manly my legs tensing up and a slight shake before and after the confertation.
Now that i study MA chances are i wont feel that as bad and still my main consern is to defuse the situation, but know i know more and have more skill i would be better prepaid for anything thus by default giving me some control over the situation making me less nurvouse and more in control and ready(i havnt had a confrentation like thise sence i started).
Now like you said that you just turned around or whatever and some one is coming to you with the intent of starting something. I would first see if its some one i know and the situation i am in, if it is some one i know i would be defencive but chances are wont feel the adrenline untill somethings tarts to happin, if i dont know this person i would first see if i am sure it is me he is after and then i would take a guarded stance, basicly a fighting stance with my front slughty towards him with my hands down and start assesing the situation: am i being surrounded, are there more of them? does he have or could have a weapon? ect ect but still i wouldnt feel teh adrenlen untill something starts to happen he yells at me or he starts swinning but i would try and make my self aware of the surrondings and his actions.