First we have to find what your issue is, because it doesn't start with your parents. I assume that there's a bit of an issue with money and standard of living and if you get caught, yes? The thing is, it's possible that you could find a way to cover this up and move on to another school, but how can you be sure you won't do the very same thing once you're not being watched?
Do you want to be a doctor? Because you know that after this year, there's just another of work and another after that and another after that. It's not exactly a great occupation to start if you're not positive you want to put that time in. Are there other fields you'd like to go into? Has part of your procrastination come from resenting the image of the lie you're living?
You may think that telling your family isn't an option, but how stupid will they permit to being and for how long? Are they paying your tuition? When you secretly apply to another med school, do you think that they'll let you right in with failing grades and an academic probation in your suitcase? What will you do if you CAN'T get in to another school right now?
I'm not admonishing your idea of secrecy. Sometimes lying can come in handy, but you have to weigh the odds here. If your family wanted to find out every grade you've made since you were 7, they can do so if they're footing the school bill. So what are the odds that you even CAN pull off that idea? And if not that idea, then what?
If you're going to have to have a conversation about this with them at some point, better to make it voluntary on your part. If you think you're panicking now, wait til you get a phone call from your family saying they know. Do you not think it better to come up with what exactly you WOULD like to do, and go tell them that you'd like to switch concentrations and/or go to a different post-grad school?
If none of that helps, and the worst happens, and you get busted and your parents disown you (which, for most parents is too hard to do) then my only advice is that you will be okay. I was you once. Slightly different circumstances, but the same problem essentially. I'm 30 now. And I'm not dead, homeless or unhappy, and my parents still love me.
All things in life can be answered by looking within. Corny and trite, but still accurate. You're never going to buckle down and do work unless there's a real motivation in it for you, and only you can know what impetus will trigger your diligence. Until you can know that, everything else will be a band-aid on the problem. I think you might be tired of running, so maybe that's something to think about.
I wish you the best luck and I'd love to hear an update.
You're not a failure. They don't ask for help.