Sorry to hear you're experiencing this. I second @Ignatius ' response and that the stress you're under does not seem to be worth the potential gains of remaining in an ill-fitting lab. That said, switching to the younger professor's lab sounds like your best bet. At the end of the day, which experience do you think will serve you best in reaching your long-term goals: sticking it out in a lab working on projects outside of your interests or taking a risk to pursue research you'll more than likely enjoy? I'm not sure how you'd list the former on a CV, so I'd take the latter any day of the week.