I second calstar on the idea about volunteering. If you can think of something you're interested in and do volunteer work for that, that would be a good use of your time. Being unable to work doesn't necessarily mean a life wasted, or getting fat because you're sitting around. There are all kinds of ways you can make your life enjoyable, meaningful to yourself or also to others, without necessarily having work to go to.
Volunteer, pursue a special interest, write the next great novel, take daily walks, become really well-read, take some informal classes in a favorite subject, perhaps even go after those school qualifications at a slower pace and without pressure now that there is none. Or just enjoy life in the other above ways.
There is no reason to feel bad about accepting the help in living that claiming benefits you are entitled to can give. You have it on authority that working life could be very hard on your mental health; you're not slacking or dodging work, you have a condition that makes it very, very difficult for you.
Try not to worry about accepting the help given to you in the form of the benefit payments. Instead pursue things you'd like to pursue. Life without school or work can still be interesting, fulfilling and useful.