Stephanie, ask for what you need girl! It will be better for both you and your employer. :) It may feel weird to bring it up, but it's totally reasonable to say, "As an introvert, I love collaborating, but I also need to recharge with a couple hours of solo work. Could we possibly find a quiet space for me to use now and then, or build in a couple of remote hours?" You won't lose a job offer over this, and I bet the right employer will love that you're asking for what you need to do your best work.
Do you have any suggestions for resources for those without access to healthcare to get help for PTSD?