Can fallin down on your back cause abortion?

Ok, so my bf and I had "sex" and he always uses a condom, but im still panicking. I think I have a regular period cuz it always comes around the same date, so about I would say 3_5 days later we had sexual intercouse, idk if I was ovulating, not sure I dont understand the cycle, but a week later I felt really bad cramps over night and I read about implantation cramps but I didnt have any spotting, a week later I fell on my back at the metro really bad, on the escalator, just today ghe whole day I feel light headed and I feel like vomitting. Im very confused! And I have been studing so much and not slept so well because I have finals at school, so not sure wwhat it can be! can those be symptoms that im pregnant or not? If so could that fall cause a misscarriage if im pregnant? Please help me out! Thanx!