Fens, i work with medical students (some are doing MD/PhD program). Getting an Excused Absence to take a semester off for illness won't ruin anything for school. you'll do better to go this route if you are overwhelmed and can't concentrate right now. they can adjust your schedule and you can flex the year.
the most important thing right now is to stop self-medicating with booze cos it is making things look WORSE and contributing to your depression and anxiety. you will feel tremendous relief when you take a step towards getting control of your life.