I have a much harder time being "productive" than people without mental illnesses because my anxiety hinders me in multiple ways. But I am also more able to be "productive" because I do not have a disability or chronic pain that constantly drains my energy.
It's also true that all people need time to relax and recharge. And that goes beyond eight hours of sleep. This is basic psychology and medical science. You can actually increase productivity by taking a few minutes to chill for every hour or even every half hour of work. Not taking enough time to relax can literally kill you. Seriously, people in Japan have literally dropped dead out of nowhere, and their deaths are attributed to constantly working their asses off. It's a little scary. Plus, stress causes all kinds of health problems.
Remember, kids. Your health - physical and mental - and your happiness are more important than you homework, or your job work, or capitalism and its shitty imaginary market. Take care of yourself! In whatever way you like best! Every day!