you probably did. you probably went into a steep dive with your head towards the ground. that means your surface area decreased. you will fall faster when that happens.
not to scare you but at terminal velocity when you reach 1800 ft youve only got a few seconds to live. I know you were OPEN at 1800ft but if you were falling through said altitude you would only have about 6-10 seconds ti live, depending on your fall rate.
heres the catch!
How long does it take your main to open? how long does it take your reserve to open? pretty scary huh?
at the risk of sounding rude, i would make the comment that this sport isn't for everyone. with everything you've mentioned that has happened to you, i haven't had that much go wrong in over 500 jumps (but, jump numbers don't mean a thing) it sounds to me like your experiencieng sensory overload, slow down and if you don't fully understand something, ask, and keep asking until you get a response that you can understand. it's hard to adlib in freefall. one more small piece of advice.....relax, and have fun with each and everyone of your sky dives. and remember, arch fixes everything!
Never thought of that God I really dont know how long either take to open but let me tell you: on my back tummy side i don't give a hoot I'm pully that handle like I never have pulled before.
thats good if youve run out of time. but if youre at 4500 and this happens STAY ALTITUDE AWARE, and try to get in a good deployment position. theres no reason to dump on your back at 4500 if you can flip over before 2500 ft