I can relate, in a way, to the fears you are having. I surrendered a job I held for 12 years, and still loved, in order to atend medical school. Although I, and my employer, always knew what my goals were, it was still difficult to leave. In a period of one month I quit my job, sold my house, gave away my belongings, said my goodbyes, and left to a country torn with conflict. A place where I had no personal, religious, or idealogical ties.
Prior to leaving, although I never had many doubts about what I wanted to do, or was going to do, I was sick at the thought of leaving my family for four years. They had often depended on me and I served as the mediator for the family and offered some degree of stability and financial support when needed. I did the most selfish thing I had ever considered, I left them for a place six thousand miles away. Their protests did nothing to change my mind, but did a lot to increase the morning nausea I experienced prior to leaving and the guilt I would later come to have. I still didn't hesitate as I boarded the plane. I was doing what I had always wanted to do.
My initial integration into my new environment was less than smoothe to say the least. For the first few months I continued to live from my suitcases. I filled my house with plants to remind me of the greenery of home. Buddhist chants resonated through my apartment at all times of the day and night. The calls I expected from my friends and long time coworkers never came...the e-mails were rather sparse as well. Academically I struggled. During my first visit home my classmates wondered if I would return. I was actually wondering the same thing. But, it all passed.
It has been three years now. My family has survived wonderfully without me and have become strong supporters as I pursue my dreams. I rarely miss my job lthough I keep in touch with my friends. Academically I am doing well. I even let all of my plants die...well, it was unintentional neglect. It has not been an easy path. The fears I had concerning medical school were never realized. The truth is, it is much easier, and harder, than you can imagine at the moment. I know, you think I contradicted myself. Let me explain. The difficulties that you have imagined, are not the ones that you are necessarily going to face. The long hours you anticipate, the days without sleep, will probably only be transient periods before exams and during a few clinical rotations. I have had more consistent sleep in medical school than I ever had before. Studying tirelessly until the wee hours of the morning are seldom required if you are at all efficient. Wondering if you were meant to be among all of the "gifted" students that are in your class will also resolve itself, there will be people stronger and weaker than yourself. You will have many opportunities to discover who you truly are. In fact, you will have an edge over your classmates that went from highschool, to college, to medical school. Most of them know little about life in the sense that you do. The maturity level was initially astounding to me, but I was surprised at how quickly our maturity levels met in the middle (Theirs increased, mine regressed).
You initial efforts should be placed on getting comfortable in you environment and making peace with yourself about your decision. The academics will take care of themselves when your thoughts are not dwelling on other things. If they let you into medical school, you are certainly capable of making it to the end. Medical school is no different than your undergraduate with the exception that the volume is increased. Someone once likened it to trying to soak up a river with a paper towel. It sometimes seems futile to even try. There is so much to learn that you will never catch it all, just do your best to soak up what you can as it rushes by.
I wish you all the best on your new journey...